Thursday 13 August 2015

Construction engineering

Construction engineering is a professional discipline that deals with the designing, planning, construction, and management of infrastructures such as highways, bridges, airports, railroads, buildings, dams, and utilities. These Engineers are unique such that they are a cross between civil engineers and construction managers. Construction engineers learn the designing aspect much like civil engineers and construction site management functions much like construction managers.
The primary difference between a construction engineer and a construction manager is that the construction engineer has the ability to sit for the Professional Engineer license (PE) whereas a construction manager cannot. At the educational level, construction managers are not as focused on design work as they are on construction procedures, methods, and people management. Their primary concern is to deliver a project on time, within budget, and of the desired quality.
The difference between a construction engineer and civil engineer is only at the educational level as both disciplines are able to sit for the PE exam giving them the same title of engineer. Civil engineering students concentrate more on the design work, gearing them toward a career as a design professional. This essentially requires them to take a multitude of design courses. Construction engineering students take design courses as well as construction management courses. This allows them to understand both the design functions as well as the building requirements needed to design and build today's infrastructures.

Work activities

Depending on which career the construction engineer has chosen to follow, an entry-level design engineer normally provides support to project managers and assist with creating conceptual designs, scopes, and cost estimates for the planning and construction of approved projects. It should be noted that a career in design work does require a professional engineer license (PE). Individuals who pursue this career path are strongly advised to sit for the Engineer In Training exam (EIT) while in college as it takes five years (4 years in USA) post graduate to obtain the PE license.
Entry-level construction manager positions are typically called project engineers or assistant project engineers. They are responsible for preparing purchasing requisitions, processing change orders, preparing monthly budgeting reports, and handling meeting minutes. The construction management position does not necessarily require a PE license; however possessing one does make the individual more marketable, as the PE license allows the individual to sign off on temporary structure designs.

Abilities

Construction engineers are problem solvers, they help create infrastructure that best meets the unique demands of its environment. They must be able to understand infrastructure life cycles and have the perspective to solve technical challenges with clarity and imagination. Therefore, individuals should have a strong understanding of maths and science, but many other skills are required, including critical and analytical thinking, time management, people management and good communication skills.

Educational requirements

Individuals looking to obtain a construction engineering degree must first ensure that the program is accredited by EAC or Technology Accreditation Commission (TAC) of the Accreditation Board for Engineering and Technology (ABET). ABET accreditation is assurance that a college or university program meets the quality standards established by the profession for which it prepares its students. In the US there are currently twenty-five programs that exist in the entire country so careful college consideration is advised.[2]
A typical construction engineering curriculum is a mixture of engineering mechanics, engineering design, construction management and general science and mathematics. This usually leads to a Bachelor of Science degree. The B.S. degree along with some design or construction experience is sufficient for most entry level positions. Graduate schools may be an option for those who want to go further in depth of the construction and engineering subjects taught at the undergraduate level. In most cases construction engineering graduates look to either civil engineering, engineering management, or business administration as a possible graduate degree.

Job prospects

Job prospects for construction engineers generally have a strong cyclical variation. For example, starting in 2008 - continuing until at least 2011 - job prospects have been poor due to the collapse of housing bubbles in many parts of the world. This sharply reduced demand for construction, forced construction professionals towards infrastructure construction and therefore increased the competition faced by established and new construction engineers. This increased competition, and a core reduction in quantity demand is in parallel with a possible shift in the demand for construction engineers due to the automation of many engineering tasks, overall resulting in reduced prospects for construction engineers. In early 2010 the United States construction industry had a 27% unemployment rate, this is nearly three times higher than the 9.7%[3] national average unemployment rate. The construction unemployment rate (including tradesmen) is comparable to the United States 1933 unemployment rate - the lowest point of the Great Depression - of 25%.[4]

International Building Code

History

Since the early 1900s, the system of building regulations in the United States was based on model building codes developed by three regional model code groups. The codes developed by the Building Officials Code Administrators International (BOCA) were used on the East Coast and throughout the Midwest of the United States, while the codes from the Southern Building Code Congress International (SBCCI) were used in the Southeast and the codes published by the International Conference of Building Officials (ICBO) covered the West Coast and across to most of the Midwest. Although regional code development has been effective and responsive to the regulatory needs of the local jurisdictions, by the early 1990s it became obvious that the country needed a single coordinated set of national model building codes. The nation’s three model code groups decided to combine their efforts and in 1994 formed the International Code Council (ICC) to develop codes that would have no regional limitations.
After three years of extensive research and development, the first edition of the International Building Code was published in 1997. The code was patterned on three legacy codes previously developed by the organizations that constitute ICC. By the year 2000, ICC had completed the International Codes series and ceased development of the legacy codes in favor of their national successor.

Legacy codes

Competing codes and final adoption

The National Fire Protection Association, initially, joined ICC in a collective effort to develop the International Fire Code (IFC). This effort however fell apart at the completion of the first draft of the document. Subsequent efforts by ICC and NFPA to reach agreement on this and other documents were unsuccessful, resulting in a series of disputes between the two organizations. After several failed attempts to find common ground with the ICC, NFPA withdrew from participation in development of the International Codes and joined with International Association of Plumbing and Mechanical Officials (IAPMO), American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and the Western Fire Chiefs Association to create an alternative set of codes. First published in 2002, the code set named the Comprehensive Consensus Codes, or C3, includes the NFPA 5000 building code as its centerpiece and the companion codes such as the National Electrical Code, NFPA 101 Life Safety Code, UPC, UMC, and NFPA 1. Unlike the IBC, the NFPA 5000 conformed to ANSI-established policies and procedures for the development of voluntary consensus standards.
The NFPA's move to introduce a competing building standard received strong opposition from powerful trade groups such as the American Institute of Architects (AIA), BOMA International and National Association of Home Builders (NAHB). Subsequent to unsuccessful attempts to encourage peaceful cooperation and resolution between NFPA and ICC on their codes disputes, a number of organizations, including AIA, BOMA and two dozen commercial real estate associations, founded the Get It Together coalition, which repeatedly urged NFPA to abandon code development related to NFPA 5000 and to work with ICC to integrate the other NFPA codes and standards into the ICC family of codes.
Initially, California adopted the NFPA 5000 codes as a baseline for the future California Building Code, but later rescinded the decision when Gov. Davis was recalled from office and Gov Schwarzenegger was elected. Upon his election, Gov. Schwarzenegger rescinded directive to use NFPA 5000, and California adopted the IBC. Adopting NFPA 5000 would cause a disparity between California and the majority of other states which had adopted IBC; not to mention, the legacy ICBO started in California and was headquartered in Whittier, CA.[1]

Overview

A large portion of the International Building Code deals with fire prevention. It differs from the related International Fire Code in that the IBC addresses fire prevention in regard to construction and design and the fire code addresses fire prevention in regard to the operation of a completed and occupied building. For example, the building code sets criteria for the number, size and location of exits in the design of a building while the fire code requires the exits of a completed and occupied building to be unblocked. The building code also deals with access for the disabled and structural stability (including earthquakes). The International Building Code applies to all structures in areas where it is adopted, except for one and two family dwellings (see International Residential Code).
Parts of the code reference other codes including the International Plumbing Code, the International Mechanical Code, the National Electric Code, and various National Fire Protection Association standards. Therefore, if a municipality adopts the International Building Code, it also adopts those parts of other codes referenced by the IBC. Often, the plumbing, mechanical, and electric codes are adopted along with the building code.
The code book itself (2000 edition) totals over 700 pages and chapters include:
  • Building occupancy classifications
  • Building heights and areas
  • Interior finishes
  • Foundation, wall, and roof construction
  • Fire protection systems (sprinkler system requirements and design)
  • Materials used in construction
  • Elevators and escalators
  • Already existing structures
  • Means of egress (see below)
Use of the term International: "Calling it 'international' keeps it from being called the 'U.S. Building Code.' explains Bill Tangye, SBCCI Chief Executive Officer. "Some U.S. Model codes are already used outside the United States. Bermuda uses BOCA, and Western Somoa uses ICBO."[2]

Means of egress

The phrase "means of egress" refers to the ability to exit the structure, primarily in the event of an emergency, such as a fire. Specifically, a means of egress is broken into three parts: the path of travel to an exit, the exit itself, and the exit discharge (the path to a safe area outside). The code also address the number of exits required for a structure based on its intended occupancy use and the number of people who could be in the place at one time as well as their relative locations. It also deals with special needs, such as hospitals, nursing homes, and prisons where evacuating people may have special requirements. In some instances, requirements are made based on possible hazards (such as in industries) where flammable or toxic chemicals will be in use.

Accessibility

"Accessibility" refers to the accommodation of physically challenged people in structures. This includes maneuvering from public transportation, building entry, parking spaces, elevators, and restrooms. This term replaces the term "handicapped" (handicapped parking, handicapped restroom) which generally found to be derogatory.
Accessibility can include domotics rules.

Existing structures

Building code requirements generally apply to the construction of new buildings and alterations or additions to existing buildings, changes in the use of buildings, and the demolition of buildings or portions of buildings at the ends of their useful or economic lives. As such, building codes obtain their effect from the voluntary decisions of property owners to erect, alter, add to, or demolish a building in a jurisdiction where a building code applies, because these circumstances routinely require a permit. The plans are subject to review for compliance with current building codes as part of the permit application process. Generally, building codes are not otherwise retroactive except to correct an imminent hazard. However, accessibility standards - similar to those referenced in the model building codes - may be retroactive subject to the applicability of the Americans with Disabilities Act (ADA) which is a federal civil rights requirement.
Alterations and additions to an existing building must usually comply with all new requirements applicable to their scope as related to the intended use of the building as defined by the adopted code (e.g., Section 101.2 Scope, International Building Code, any version). Some changes in the use of a building often expose the entire building to the requirement to comply fully with provisions of the code applicable to the new use because the applicability of the code is use-specific. A change in use usually changes the applicability of code requirements and as such, will subject the building to review for compliance with the currently applicable codes (refer to Section 3408, Change of Occupancy, International Building Code - 2009). The applicability of codes and/or specific requirements of the codes are subject to potential amendments as specified by the authority that adopts the code (refer to Section 104, International Building Code, any version). Some jurisdictions[which?] limit such application to matters of fire safety, disabled access or structural integrity, others apply an economic feasibility or practicality test, and still others exempt buildings of special use or architectural or historic significance.[citation needed]
Existing buildings are not exempt from new requirements, especially those considered essential to achieve health, safety or general welfare objectives of the adopting jurisdiction, even when they are not otherwise subject to alteration, addition, change in use, or demolition.[citation needed] Such requirements typically remedy existing conditions, considered in hindsight, inimical to safety, such as the lack of automatic fire sprinklers in certain places of assembly, as became a major concern[citation needed] after the Station nightclub fire in 2003 killed 100 people.
Although such remedial enactments address existing conditions, they do not violate the United States Constitution's ban on the adoption of ex post facto law, as they do not criminalize or seek to punish past conduct.[citation needed] Such requirements merely prohibit the maintenance or continuance of conditions that would prove injurious to a member of the public or the broader public interest.[citation needed]
Assertions by property rights advocates in the United States[who?] that such requirements violate the "takings clause" of the Fifth Amendment to the United States Constitution, have generally failed on grounds that compliance with such requirements increases rather than decreases the capital value of the property concerned.[citation needed]
Some states,[which?] especially those that delegate their adoption and enforcement authority to subordinate local jurisdictions, may exempt their own buildings from compliance with local building codes or local amendments to a statewide building code.[citation needed] Similarly, property owned by the United States Government is considered exempt from state and local enactments, although such properties are generally not exempt from inspection by state or local authorities, except on grounds of protecting national defense or national security.[citation needed] In lieu of submitting themselves to compliance with the requirements of other government jurisdictions, most state and federal agencies[which?] adopt construction and maintenance requirements that either reference model building codes or model their provisions on their requirements.[citation needed]
Some jurisdictions[which?] have enacted requirements to bring certain types or uses of existing buildings into compliance with new requirements, such as the installation of smoke alarms in households or dwelling units, at the time of sale. Some safety advocates[who?] have suggested a similar approach to encourage remedial application of other requirements, but few jurisdictions have found it economical or equitable to disincentivise property transactions in this way.[citation needed]
Many jurisdictions have found the application of new requirements to old, particularly historic buildings, challenging. New Jersey, for example, has adopted specific state amendments (see New Jersey's Rehabilitation Subcode)to provide a means of code compliance to existing structures without forcing the owner to comply with rigid requirements of the currently adopted Building Codes where it may be technically infeasible to do so. California has also enacted a specific historic building code (see 2001 California Historic Building Code). Other states[which?] require compliance with building and fire codes, subject to reservations, limitations, or jurisdictional discretion to protect historic building stock as a condition of nominating or listing a building for preservation or landmark status, especially where such status attracts tax credits, investment of public money, or other incentives.
The listing of a building on the National Register of Historic Places does not exempt it from compliance with state or local building code requirements.[citation needed]

Updating cycle

Updated editions of the IBC are published on a three year cycle (2000, 2003, 2006…). This fixed schedule has led other organizations, which produce referenced standards, to align their publishing schedule with that of the IBC.[citation needed]

Referenced standards

Model building codes rely heavily on referenced standards as published and promulgated by other standards organizations such as ASTM (ASTM International), ANSI (American National Standards Institute), and NFPA (National Fire Protection Association). The structural provisions rely heavily on referenced standards, such as the Minimum Design Loads for Buildings and Structures published by the American Society of Civil Engineers (ASCE-7).
Changes in parts of the reference standard can result in disconnection between the corresponding editions of the reference standards.

Copyright controversy

Many states or municipalities in the United States of America adopt the ICC family of codes.
In the wake of the Federal copyright case Veeck v. Southern Building Code Congress Int'l, Inc.,[3] the organization Public Resource has published a substantial portion of the enacted building codes on-line, and they are available as PDFs.[4]

ICC building codes

  • International Building Code
  • International Fire Code
  • International Plumbing Code
  • International Mechanical Code
  • International Fuel Gas Code
  • International Energy Conservation Code
  • ICC Performance Code
  • International Wildland Urban Interface Code
  • International Existing Building Code
  • International Property Maintenance Code
  • International Private Sewage Disposal Code
  • International Zoning Code
  • International Green Construction Code

Earthquake engineering

Earthquake engineering or seismic engineering is the scientific field concerned with protecting society, the natural environment, and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels.[1] Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to seismic loading; it is considered as a subset of both structural and geotechnical engineering. However, the tremendous costs experienced in recent earthquakes have led to an expansion of its scope to encompass disciplines from the wider field of civil engineering and from the social sciences, especially sociology, political science, economics and finance.
The main objectives of earthquake engineering are:
  • Foresee the potential consequences of strong earthquakes on urban areas and civil infrastructure.
  • Design, construct and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes.[2]
A properly engineered structure does not necessarily have to be extremely strong or expensive. It has to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage.

Seismic loading

Taipei 101, equipped with a tuned mass damper, is one of the world's tallest skyscrapers.
Main article: Seismic loading
Seismic loading means application of an earthquake-generated excitation on a structure (or geo-structure). It happens at contact surfaces of a structure either with the ground,[4] with adjacent structures,[5] or with gravity waves from tsunami.

Seismic performance

Main article: Seismic analysis
Earthquake or seismic performance defines a structure's ability to sustain its main functions, such as its safety and serviceability, at and after a particular earthquake exposure. A structure is normally considered safe if it does not endanger the lives and well-being of those in or around it by partially or completely collapsing. A structure may be considered serviceable if it is able to fulfill its operational functions for which it was designed.
Basic concepts of the earthquake engineering, implemented in the major building codes, assume that a building should survive a rare, very severe earthquake by sustaining significant damage but without globally collapsing.[6] On the other hand, it should remain operational for more frequent, but less severe seismic events.

Seismic performance assessment

Engineers need to know the quantified level of the actual or anticipated seismic performance associated with the direct damage to an individual building subject to a specified ground shaking. Such an assessment may be performed either experimentally or analytically.

Experimental assessment

Experimental evaluations are expensive tests that are typically done by placing a (scaled) model of the structure on a shake-table that simulates the earth shaking and observing its behavior.[7] Such kinds of experiments were first performed more than a century ago.[8] Only recently has it become possible to perform 1:1 scale testing on full structures.
Due to the costly nature of such tests, they tend to be used mainly for understanding the seismic behavior of structures, validating models and verifying analysis methods. Thus, once properly validated, computational models and numerical procedures tend to carry the major burden for the seismic performance assessment of structures.

Analytical/Numerical Assessment

Snapshot from shake-table video of a 6-story non-ductile concrete building destructive testing
Seismic performance assessment or seismic structural analysis is a powerful tool of earthquake engineering which utilizes detailed modelling of the structure together with methods of structural analysis to gain a better understanding of seismic performance of building and non-building structures. The technique as a formal concept is a relatively recent development.
In general, seismic structural analysis is based on the methods of structural dynamics.[9] For decades, the most prominent instrument of seismic analysis has been the earthquake response spectrum method which also contributed to the proposed building code's concept of today.[10]
However, such methods are good only for linear elastic systems, being largely unable to model the structural behavior when damage (i.e., non-linearity) appears. Numerical step-by-step integration proved to be a more effective method of analysis for multi-degree-of-freedom structural systems with significant non-linearity under a transient process of ground motion excitation.[11]
Basically, numerical analysis is conducted in order to evaluate the seismic performance of buildings. Performance evaluations are generally carried out by using nonlinear static pushover analysis or nonlinear time-history analysis. In such analyses, it is essential to achieve accurate non-linear modeling of structural components such as beams, columns, beam-column joints, shear walls etc. Thus, experimental results play an important role in determining the modeling parameters of individual components, especially those that are subject to significant non-linear deformations. The individual components are then assembled to create a full non-linear model of the structure. Thus created models are analyzed to evaluate the performance of buildings.
The capabilities of the structural analysis software are a major consideration in the above process as they restrict the possible component models, the analysis methods available and, most importantly, the numerical robustness. The latter becomes a major consideration for structures that venture into the non-linear range and approach global or local collapse as the numerical solution becomes increasingly unstable and thus difficult to reach. There are several commercially available Finite Element Analysis software's such as CSI-SAP2000 and CSI-PERFORM-3D and Scia Engineer-ECtools which can be used for the seismic performance evaluation of buildings. Moreover, there is research-based finite element analysis platforms such as OpenSees, RUAUMOKO and the older DRAIN-2D/3D, several of which are now open source.

Research for earthquake engineering

Research for earthquake engineering means both field and analytical investigation or experimentation intended for discovery and scientific explanation of earthquake engineering related facts, revision of conventional concepts in the light of new findings, and practical application of the developed theories.
The National Science Foundation (NSF) is the main United States government agency that supports fundamental research and education in all fields of earthquake engineering. In particular, it focuses on experimental, analytical and computational research on design and performance enhancement of structural systems.
E-Defense Shake Table[12]
The Earthquake Engineering Research Institute (EERI) is a leader in dissemination of earthquake engineering research related information both in the U.S. and globally.
A definitive list of earthquake engineering research related shaking tables around the world may be found in Experimental Facilities for Earthquake Engineering Simulation Worldwide.[13] The most prominent of them is now E-Defense Shake Table[14] in Japan.

Major U.S. research programs

Large High Performance Outdoor Shake Table, UCSD, NEES network
NSF also supports the George E. Brown, Jr. Network for Earthquake Engineering Simulation
The NSF Hazard Mitigation and Structural Engineering program (HMSE) supports research on new technologies for improving the behavior and response of structural systems subject to earthquake hazards; fundamental research on safety and reliability of constructed systems; innovative developments in analysis and model based simulation of structural behavior and response including soil-structure interaction; design concepts that improve structure performance and flexibility; and application of new control techniques for structural systems.[15]
(NEES) that advances knowledge discovery and innovation for earthquakes and tsunami loss reduction of the nation's civil infrastructure and new experimental simulation techniques and instrumentation.[16]
The NEES network features 14 geographically-distributed, shared-use laboratories that support several types of experimental work:[16] geotechnical centrifuge research, shake-table tests, large-scale structural testing, tsunami wave basin experiments, and field site research.[17] Participating universities include: Cornell University; Lehigh University; Oregon State University; Rensselaer Polytechnic Institute; University at Buffalo, State University of New York; University of California, Berkeley; University of California, Davis; University of California, Los Angeles; University of California, San Diego; University of California, Santa Barbara; University of Illinois, Urbana-Champaign; University of Minnesota; University of Nevada, Reno; and the University of Texas, Austin.[16]
NEES at Buffalo testing facility
The equipment sites (labs) and a central data repository are connected to the global earthquake engineering community via the NEEShub website. The NEES website is powered by HUBzero software developed at Purdue University for nanoHUB specifically to help the scientific community share resources and collaborate. The cyberinfrastructure, connected via Internet2, provides interactive simulation tools, a simulation tool development area, a curated central data repository, animated presentations, user support, telepresence, mechanism for uploading and sharing resources, and statistics about users and usage patterns.
This cyberinfrastructure allows researchers to: securely store, organize and share data within a standardized framework in a central location; remotely observe and participate in experiments through the use of synchronized real-time data and video; collaborate with colleagues to facilitate the planning, performance, analysis, and publication of research experiments; and conduct computational and hybrid simulations that may combine the results of multiple distributed experiments and link physical experiments with computer simulations to enable the investigation of overall system performance.
These resources jointly provide the means for collaboration and discovery to improve the seismic design and performance of civil and mechanical infrastructure systems.

Earthquake simulation

The very first earthquake simulations were performed by statically applying some horizontal inertia forces based on scaled peak ground accelerations to a mathematical model of a building.[18] With the further development of computational technologies, static approaches began to give way to dynamic ones.
Dynamic experiments on building and non-building structures may be physical, like shake-table testing, or virtual ones. In both cases, to verify a structure's expected seismic performance, some researchers prefer to deal with so called "real time-histories" though the last cannot be "real" for a hypothetical earthquake specified by either a building code or by some particular research requirements. Therefore, there is a strong incentive to engage an earthquake simulation which is the seismic input that possesses only essential features of a real event.
Sometimes earthquake simulation is understood as a re-creation of local effects of a strong earth shaking.

Structure simulation

Concurrent experiments with two building models which are kinematically equivalent to a real prototype.[19]
Theoretical or experimental evaluation of anticipated seismic performance mostly requires a structure simulation which is based on the concept of structural likeness or similarity. Similarity is some degree of analogy or resemblance between two or more objects. The notion of similarity rests either on exact or approximate repetitions of patterns in the compared items.
In general, a building model is said to have similarity with the real object if the two share geometric similarity, kinematic similarity and dynamic similarity. The most vivid and effective type of similarity is the kinematic one. Kinematic similarity exists when the paths and velocities of moving particles of a model and its prototype are similar.
The ultimate level of kinematic similarity is kinematic equivalence when, in the case of earthquake engineering, time-histories of each story lateral displacements of the model and its prototype would be the same.

Seismic vibration control

Seismic vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures. All seismic vibration control devices may be classified as passive, active or hybrid[20] where:
  • passive control devices have no feedback capability between them, structural elements and the ground;
  • active control devices incorporate real-time recording instrumentation on the ground integrated with earthquake input processing equipment and actuators within the structure;
  • hybrid control devices have combined features of active and passive control systems.[21]
When ground seismic waves reach up and start to penetrate a base of a building, their energy flow density, due to reflections, reduces dramatically: usually, up to 90%. However, the remaining portions of the incident waves during a major earthquake still bear a huge devastating potential.
After the seismic waves enter a superstructure, there are a number of ways to control them in order to soothe their damaging effect and improve the building's seismic performance, for instance:
  • to disperse the wave energy between a wider range of frequencies;
Mausoleum of Cyrus, the oldest base-isolated structure in the world
Devices of the last kind, abbreviated correspondingly as TMD for the tuned (passive), as AMD for the active, and as HMD for the hybrid mass dampers, have been studied and installed in high-rise buildings, predominantly in Japan, for a quarter of a century.[23]
However, there is quite another approach: partial suppression of the seismic energy flow into the superstructure known as seismic or base isolation.
For this, some pads are inserted into or under all major load-carrying elements in the base of the building which should substantially decouple a superstructure from its substructure resting on a shaking ground.
The first evidence of earthquake protection by using the principle of base isolation was discovered in Pasargadae, a city in ancient Persia, now Iran, and dates back to 6th century BCE. Below, there are some samples of seismic vibration control technologies of today.

Dry-stone walls control

Dry-stone walls of Machu Picchu Temple of the Sun, Peru
People of Inca civilization were masters of the polished 'dry-stone walls', called ashlar, where blocks of stone were cut to fit together tightly without any mortar. The Incas were among the best stonemasons the world has ever seen[24] and many junctions in their masonry were so perfect that even blades of grass could not fit between the stones.
Peru is a highly seismic land and for centuries the mortar-free construction proved to be apparently more earthquake-resistant than using mortar. The stones of the dry-stone walls built by the Incas could move slightly and resettle without the walls collapsing, a passive structural control technique employing both the principle of energy dissipation and that of suppressing resonant amplifications.[25]

Lead rubber bearing

LRB being tested at the UCSD Caltrans-SRMD facility
Lead Rubber Bearing or LRB is a type of base isolation employing a heavy damping. It was invented by Bill Robinson, a New Zealander.[26]
Heavy damping mechanism incorporated in vibration control technologies and, particularly, in base isolation devices, is often considered a valuable source of suppressing vibrations thus enhancing a building's seismic performance. However, for the rather pliant systems such as base isolated structures, with a relatively low bearing stiffness but with a high damping, the so-called "damping force" may turn out the main pushing force at a strong earthquake. The video[27] shows a Lead Rubber Bearing being tested at the UCSD Caltrans-SRMD facility. The bearing is made of rubber with a lead core. It was a uniaxial test in which the bearing was also under a full structure load. Many buildings and bridges, both in New Zealand and elsewhere, are protected with lead dampers and lead and rubber bearings. Te Papa Tongarewa, the national museum of New Zealand, and the New Zealand Parliament Buildings have been fitted with the bearings. Both are in Wellington which sits on an active earthquake fault.[26]

Tuned mass damper

Main article: Tuned mass damper
Tuned mass damper in Taipei 101, the world's third tallest skyscraper
Typically the tuned mass dampers are huge concrete blocks mounted in skyscrapers or other structures and moved in opposition to the resonance frequency oscillations of the structures by means of some sort of spring mechanism.
Taipei 101 skyscraper needs to withstand typhoon winds and earthquake tremors common in its area of the Asia-Pacific. For this purpose, a steel pendulum weighing 660 metric tones that serves as a tuned mass damper was designed and installed atop the structure. Suspended from the 92nd to the 88th floor, the pendulum sways to decrease resonant amplifications of lateral displacements in the building caused by earthquakes and strong gusts.

Friction pendulum bearing

FPB[28] shake-table testing
Friction Pendulum Bearing (FPB) is another name of Friction Pendulum System (FPS). It is based on three pillars:[29]
  • articulated friction slider;
  • spherical concave sliding surface;
  • enclosing cylinder for lateral displacement restraint.
Snapshot with the link to video clip of a shake-table testing of FPB system supporting a rigid building model is presented at the right.

Building elevation control

Building elevation control is a valuable source of vibration control of seismic loading. Pyramid-shaped skyscrapers continue to attract the attention of architects and engineers because such structures promise a better stability against earthquakes and winds. The elevation configuration can prevent buildings' resonant amplifications because a properly configured building disperses the shear wave energy between a wide range of frequencies.
Earthquake or wind quieting ability of the elevation configuration is provided by a specific pattern of multiple reflections and transmissions of vertically propagating waves, which are generated by breakdowns into homogeneity of story layers, and a taper. Any abrupt changes of the propagating waves velocity result in a considerable dispersion of the wave energy between a wide ranges of frequencies thus preventing the resonant displacement amplifications in the building.
A tapered profile of a building is not a compulsory feature of this method of structural control. A similar resonance preventing effect can be also obtained by a proper tapering of other characteristics of a building structure, namely, its mass and stiffness. As a result, the building elevation configuration techniques permit an architectural design that may be both attractive and functional (see, e.g., Pyramid).

Simple roller bearing

Simple roller bearing is a base isolation device which is intended for protection of various building and non-building structures against potentially damaging lateral impacts of strong earthquakes.
This metallic bearing support may be adapted, with certain precautions, as a seismic isolator to skyscrapers and buildings on soft ground. Recently, it has been employed under the name of Metallic Roller Bearing for a housing complex (17 stories) in Tokyo, Japan.[30]

Springs-with-damper base isolator

Springs-with-damper close-up
Springs-with-damper base isolator installed under a three-story town-house, Santa Monica, California is shown on the photo taken prior to the 1994 Northridge earthquake exposure. It is a base isolation device conceptually similar to Lead Rubber Bearing.
One of two three-story town-houses like this, which was well instrumented for recording of both vertical and horizontal accelerations on its floors and the ground, has survived a severe shaking during the Northridge earthquake and left valuable recorded information for further study.

Hysteretic damper

Hysteretic damper is intended to provide better and more reliable seismic performance than that of a conventional structure at the expense of the seismic input energy dissipation.[31] There are four major groups of hysteretic dampers used for the purpose, namely:
  • Fluid viscous dampers (FVDs)
  • Metallic yielding dampers (MYDs)
  • Viscoelastic dampers (VEDs)
  • Friction dampers (FDs)
  • Straddlingpendulum dampers (swing)
Each group of dampers has specific characteristics, advantages and disadvantages for structural applications.

Seismic design

Seismic design is based on authorized engineering procedures, principles and criteria meant to design or retrofit structures subject to earthquake exposure.[18] Those criteria are only consistent with the contemporary state of the knowledge about earthquake engineering structures.[32] Therefore, a building design which exactly follows seismic code regulations does not guarantee safety against collapse or serious damage.[33]
The price of poor seismic design may be enormous. Nevertheless, seismic design has always been a trial and error process whether it was based on physical laws or on empirical knowledge of the structural performance of different shapes and materials.
San Francisco after the 1906 earthquake and fire
To practice seismic design, seismic analysis or seismic evaluation of new and existing civil engineering projects, an engineer should, normally, pass examination on Seismic Principles[34] which, in the State of California, include:
  • Seismic Data and Seismic Design Criteria
  • Seismic Characteristics of Engineered Systems
  • Seismic Forces
  • Seismic Analysis Procedures
  • Seismic Detailing and Construction Quality Control
To build up complex structural systems,[35] seismic design largely uses the same relatively small number of basic structural elements (to say nothing of vibration control devices) as any non-seismic design project.
Normally, according to building codes, structures are designed to "withstand" the largest earthquake of a certain probability that is likely to occur at their location. This means the loss of life should be minimized by preventing collapse of the buildings.
Seismic design is carried out by understanding the possible failure modes of a structure and providing the structure with appropriate strength, stiffness, ductility, and configuration[36] to ensure those modes cannot occur.

Seismic design requirements

Seismic design requirements depend on the type of the structure, locality of the project and its authorities which stipulate applicable seismic design codes and criteria.[6] For instance, California Department of Transportation's requirements called The Seismic Design Criteria (SDC) and aimed at the design of new bridges in California[37] incorporate an innovative seismic performance-based approach.
The most significant feature in the SDC design philosophy is a shift from a force-based assessment of seismic demand to a displacement-based assessment of demand and capacity. Thus, the newly adopted displacement approach is based on comparing the elastic displacement demand to the inelastic displacement capacity of the primary structural components while ensuring a minimum level of inelastic capacity at all potential plastic hinge locations.
In addition to the designed structure itself, seismic design requirements may include a ground stabilization underneath the structure: sometimes, heavily shaken ground breaks up which leads to collapse of the structure sitting upon it.[39] The following topics should be of primary concerns: liquefaction; dynamic lateral earth pressures on retaining walls; seismic slope stability; earthquake-induced settlement.[40]
Nuclear facilities should not jeopardise their safety in case of earthquakes or other hostile external events. Therefore, their seismic design is based on criteria far more stringent than those applying to non-nuclear facilities.[41] The Fukushima I nuclear accidents and damage to other nuclear facilities that followed the 2011 Tōhoku earthquake and tsunami have, however, drawn attention to ongoing concerns over Japanese nuclear seismic design standards and caused other many governments to re-evaluate their nuclear programs. Doubt has also been expressed over the seismic evaluation and design of certain other plants, including the Fessenheim Nuclear Power Plant in France.

Failure modes

Failure mode is the manner by which an earthquake induced failure is observed. It, generally, describes the way the failure occurs. Though costly and time consuming, learning from each real earthquake failure remains a routine recipe for advancement in seismic design methods. Below, some typical modes of earthquake-generated failures are presented.
Typical damage to unreinforced masonry buildings at earthquakes
The lack of reinforcement coupled with poor mortar and inadequate roof-to-wall ties can result in substantial damage to an unreinforced masonry building. Severely cracked or leaning walls are some of the most common earthquake damage. Also hazardous is the damage that may occur between the walls and roof or floor diaphragms. Separation between the framing and the walls can jeopardize the vertical support of roof and floor systems.
Soft story collapse due to inadequate shear strength at ground level, Loma Prieta earthquake
Soft story effect. Absence of adequate shear walls on the ground level caused damage to this structure. A close examination of the image reveals that the rough board siding, once covered by a brick veneer, has been completely dismantled from the studwall. Only the rigidity of the floor above combined with the support on the two hidden sides by continuous walls, not penetrated with large doors as on the street sides, is preventing full collapse of the structure.
Soil liquefaction. In the cases where the soil consists of loose granular deposited materials with the tendency to develop excessive hydrostatic pore water pressure of sufficient magnitude and compact, liquefaction of those loose saturated deposits may result in non-uniform settlements and tilting of structures. This caused major damage to thousands of buildings in Niigata, Japan during the 1964 earthquake.[42]
Car smashed by landslide rock, 2008 Sichuan earthquake
Landslide rock fall. A landslide is a geological phenomenon which includes a wide range of ground movement, including rock falls. Typically, the action of gravity is the primary driving force for a landslide to occur though in this case there was another contributing factor which affected the original slope stability: the landslide required an earthquake trigger before being released.
Effects of pounding against adjacent building, Loma Prieta
Pounding against adjacent building. This is a photograph of the collapsed five-story tower, St. Joseph's Seminary, Los Altos, California which resulted in one fatality. During Loma Prieta earthquake, the tower pounded against the independently vibrating adjacent building behind. A possibility of pounding depends on both buildings' lateral displacements which should be accurately estimated and accounted for.
Effects of completely shattered joints of concrete frame, Northridge
At Northridge earthquake, the Kaiser Permanente concrete frame office building had joints completely shattered, revealing inadequate confinement steel, which resulted in the second story collapse. In the transverse direction, composite end shear walls, consisting of two wythes of brick and a layer of shotcrete that carried the lateral load, peeled apart because of inadequate through-ties and failed.
7-story reinforced concrete buildings on steep slope collapse due to the following:[43]
  • Poor detailing of the reinforcement (lack of concrete confinement in the columns and at the beam-column joints, inadequate splice length).
shifting from foundation, Whittier
Sliding off foundations effect of a relatively rigid residential building structure during 1987 Whittier Narrows earthquake. The magnitude 5.9 earthquake pounded the Garvey West Apartment building in Monterey Park, California and shifted its superstructure about 10 inches to the east on its foundation.
Earthquake damage in Pichilemu.
If a superstructure is not mounted on a base isolation system, its shifting on the basement should be prevented.
Insufficient shear reinforcement let main rebars to buckle, Northridge
Reinforced concrete column burst at Northridge earthquake due to insufficient shear reinforcement mode which allows main reinforcement to buckle outwards. The deck unseated at the hinge and failed in shear. As a result, the La Cienega-Venice underpass section of the 10 Freeway collapsed.
Support-columns and upper deck failure, Loma Prieta earthquake
Loma Prieta earthquake: side view of reinforced concrete support-columns failure which triggered the upper deck collapse onto the lower deck of the two-level Cypress viaduct of Interstate Highway 880, Oakland, CA.
Failure of retaining wall due to ground movement, Loma Prieta
Retaining wall failure at Loma Prieta earthquake in Santa Cruz Mountains area: prominent northwest-trending extensional cracks up to 12 cm (4.7 in) wide in the concrete spillway to Austrian Dam, the north abutment.
Lateral spreading mode of ground failure, Loma Prieta
Ground shaking triggered soil liquefaction in a subsurface layer of sand, producing differential lateral and vertical movement in an overlying carapace of unliquified sand and silt. This mode of ground failure, termed lateral spreading, is a principal cause of liquefaction-related earthquake damage.[44]
Beams and pier columns diagonal cracking, 2008 Sichuan earthquake
Severely damaged building of Agriculture Development Bank of China after 2008 Sichuan earthquake: most of the beams and pier columns are sheared. Large diagonal cracks in masonry and veneer are due to in-plane loads while abrupt settlement of the right end of the building should be attributed to a landfill which may be hazardous even without any earthquake.[45]
Twofold tsunami impact: sea waves hydraulic pressure and inundation. Thus, the Indian Ocean earthquake of December 26, 2004, with the epicenter off the west coast of Sumatra, Indonesia, triggered a series of devastating tsunamis, killing more than 230,000 people in eleven countries by inundating surrounding coastal communities with huge waves up to 30 meters (100 feet) high.[47]

Earthquake-resistant construction

Earthquake construction means implementation of seismic design to enable building and non-building structures to live through the anticipated earthquake exposure up to the expectations and in compliance with the applicable building codes.
Construction of Pearl River Tower X-bracing to resist lateral forces of earthquakes and winds
Design and construction are intimately related. To achieve a good workmanship, detailing of the members and their connections should be as simple as possible. As any construction in general, earthquake construction is a process that consists of the building, retrofitting or assembling of infrastructure given the construction materials available.[48]
The destabilizing action of an earthquake on constructions may be direct (seismic motion of the ground) or indirect (earthquake-induced landslides, soil liquefaction and waves of tsunami).
A structure might have all the appearances of stability, yet offer nothing but danger when an earthquake occurs.[49] The crucial fact is that, for safety, earthquake-resistant construction techniques are as important as quality control and using correct materials. Earthquake contractor should be registered in the state of the project location, bonded and insured[citation needed].
To minimize possible losses, construction process should be organized with keeping in mind that earthquake may strike any time prior to the end of construction.
Each construction project requires a qualified team of professionals who understand the basic features of seismic performance of different structures as well as construction management.

Adobe structures

Partially collapsed adobe building in Westmorland, California
Around thirty percent of the world's population lives or works in earth-made construction.[50] Adobe type of mud bricks is one of the oldest and most widely used building materials. The use of adobe is very common in some of the world's most hazard-prone regions, traditionally across Latin America, Africa, Indian subcontinent and other parts of Asia, Middle East and Southern Europe.
Adobe buildings are considered very vulnerable at strong quakes.[51] However, multiple ways of seismic strengthening of new and existing adobe buildings are available.[52]
Key factors for the improved seismic performance of adobe construction are:
  • Quality of construction.
  • Compact, box-type layout.
  • Seismic reinforcement.[53]

Limestone and sandstone structures

Base-isolated City and County Building, Salt Lake City, Utah
Limestone is very common in architecture, especially in North America and Europe. Many landmarks across the world are made of limestone. Many medieval churches and castles in Europe are made of limestone and sandstone masonry. They are the long-lasting materials but their rather heavy weight is not beneficial for adequate seismic performance.
Application of modern technology to seismic retrofitting can enhance the survivability of unreinforced masonry structures. As an example, from 1973 to 1989, the Salt Lake City and County Building in Utah was exhaustively renovated and repaired with an emphasis on preserving historical accuracy in appearance. This was done in concert with a seismic upgrade that placed the weak sandstone structure on base isolation foundation to better protect it from earthquake damage.

Timber frame structures

Anne Hvide's House, Denmark (1560)
Timber framing dates back thousands of years, and has been used in many parts of the world during various periods such as ancient Japan, Europe and medieval England in localities where timber was in good supply and building stone and the skills to work it were not.
The use of timber framing in buildings provides their complete skeletal framing which offers some structural benefits as the timber frame, if properly engineered, lends itself to better seismic survivability.[54]

Light-frame structures

A two-story wooden-frame for a residential building structure
Light-frame structures usually gain seismic resistance from rigid plywood shear walls and wood structural panel diaphragms.[55] Special provisions for seismic load-resisting systems for all engineered wood structures requires consideration of diaphragm ratios, horizontal and vertical diaphragm shears, and connector/fastener values. In addition, collectors, or drag struts, to distribute shear along a diaphragm length are required.

Reinforced masonry structures

Reinforced hollow masonry wall
A construction system where steel reinforcement is embedded in the mortar joints of masonry or placed in holes and after filled with concrete or grout is called reinforced masonry.[56]
The devastating 1933 Long Beach earthquake revealed that masonry construction should be improved immediately. Then, the California State Code made the reinforced masonry mandatory.
There are various practices and techniques to achieve reinforced masonry. The most common type is the reinforced hollow unit masonry. The effectiveness of both vertical and horizontal reinforcement strongly depends on the type and quality of the masonry, i.e. masonry units and mortar.
To achieve a ductile behavior of masonry, it is necessary that the shear strength of the wall is greater than the flexural strength.[57]

Reinforced concrete structures

Stressed Ribbon pedestrian bridge over the Rogue River, Grants Pass, Oregon
Prestressed concrete cable-stayed bridge over Yangtze river
Reinforced concrete is concrete in which steel reinforcement bars (rebars) or fibers have been incorporated to strengthen a material that would otherwise be brittle. It can be used to produce beams, columns, floors or bridges.
Prestressed concrete is a kind of reinforced concrete used for overcoming concrete's natural weakness in tension. It can be applied to beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the concrete compression member would, otherwise, experience due to a bending load.
To prevent catastrophic collapse in response earth shaking (in the interest of life safety), a traditional reinforced concrete frame should have ductile joints. Depending upon the methods used and the imposed seismic forces, such buildings may be immediately usable, require extensive repair, or may have to be demolished.

Prestressed structures

Prestressed structure is the one whose overall integrity, stability and security depend, primarily, on a prestressing. Prestressing means the intentional creation of permanent stresses in a structure for the purpose of improving its performance under various service conditions.[58]
Naturally pre-compressed exterior wall of Colosseum, Rome
There are the following basic types of prestressing:
  • Pre-compression (mostly, with the own weight of a structure)
  • Pretensioning with high-strength embedded tendons
  • Post-tensioning with high-strength bonded or unbonded tendons
Today, the concept of prestressed structure is widely engaged in design of buildings, underground structures, TV towers, power stations, floating storage and offshore facilities, nuclear reactor vessels, and numerous kinds of bridge systems.[59]
A beneficial idea of prestressing was, apparently, familiar to the ancient Rome architects; look, e.g., at the tall attic wall of Colosseum working as a stabilizing device for the wall piers beneath.

Steel structures

Collapsed section of the San Francisco – Oakland Bay Bridge in response to Loma Prieta earthquake
Steel structures are considered mostly earthquake resistant but some failures have occurred. A great number of welded steel moment-resisting frame buildings, which looked earthquake-proof, surprisingly experienced brittle behavior and were hazardously damaged in the 1994 Northridge earthquake.[60] After that, the Federal Emergency Management Agency (FEMA) initiated development of repair techniques and new design approaches to minimize damage to steel moment frame buildings in future earthquakes.[61]
For structural steel seismic design based on Load and Resistance Factor Design (LRFD) approach, it is very important to assess ability of a structure to develop and maintain its bearing resistance in the inelastic range. A measure of this ability is ductility, which may be observed in a material itself, in a structural element, or to a whole structure.
As a consequence of Northridge earthquake experience, the American Institute of Steel Construction has introduced AISC 358 "Pre-Qualified Connections for Special and intermediate Steel Moment Frames." The AISC Seismic Design Provisions require that all Steel Moment Resisting Frames employ either connections contained in AISC 358, or the use of connections that have been subjected to pre-qualifying cyclic testing.[62]

Prediction of earthquake losses

Earthquake loss estimation is usually defined as a Damage Ratio (DR) which is a ratio of the earthquake damage repair cost to the total value of a building.[63] Probable Maximum Loss (PML) is a common term used for earthquake loss estimation, but it lacks a precise definition. In 1999, ASTM E2026 'Standard Guide for the Estimation of Building Damageability in Earthquakes' was produced in order to standardize the nomenclature for seismic loss estimation, as well as establish guidelines as to the review process and qualifications of the reviewer.[64]
Earthquake loss estimations are also referred to as Seismic Risk Assessments. The risk assessment process generally involves determining the probability of various ground motions coupled with the vulnerability or damage of the building under those ground motions. The results are defined as a percent of building replacement value.[65]