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BUILDING CODES

P G A G R G T G 4

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EARTHQUAKE PROVISIONS IN

BUILDING CODES

14.1 INTRODUCTION

This last chapter presents a discussion of the role of building codes in geotechnical earth-quake engineering. The geotechnical engineer should always review local building codesand other regulatory specifications that may govern the seismic design of the project. Typesof information that could be included in the building code are as follows:

1. Earthquake potential: The building code may specify the earthquake potential fora given site. For example, Fig. 5.17 presents the seismic zone map for the United States(Uniform Building Code 1997). The seismic potential often changes as new earthquake dataare evaluated. For example, as discussed in Sec. 3.4.3, one of the main factors that con-tributed to the damage at the Port of Kobe during the Kobe earthquake was that the area hadbeen previously considered to have a relatively low seismic risk, hence the earthquakedesign criteria were less stringent than in other areas of Japan.

2. General requirements: The building code could also specify general requirementsthat must be fulfilled by the geotechnical engineer. An example is presented in Sec. 1.1,where the Uniform Building Code (1997) requires an analysis of the potential for soil liq-uefaction and soil strength loss during an earthquake. This code provision also requires thatthe geotechnical engineer evaluate the potential consequences of any liquefaction and soilstrength loss, including the estimation of differential settlement, lateral movement, andreduction in foundation bearing capacity, and discuss mitigating measures.

3. Detailed analyses: The building code could also provide detailed seismic analyses.For example, Sec. 11.5 outlines the method that can be used to determine the response spec-trum per the Uniform Building Code (1997).

14.2 CODE DEVELOPMENT

One of the most important ways to develope code is to observe the performance of struc-tures during earthquakes. There must be a desire to improve conditions and not simplyaccept the death and destruction from earthquakes as inevitable. Two examples of theimpact of earthquakes on codes and regulations are as follows:

1. March 10, 1933, Long Beach earthquake in California: This earthquake brought anend to the practice of laying brick masonry without reinforcing steel. Prior to this earthquake,

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the exterior walls of buildings were often of brick, or in some cases hollow clay tile. Woodwas used to construct the roofs and floors, which were supported by the brick walls. Thistype of construction was used for schools, and the destruction to these schools was some of the most spectacular damage during the 1933 Long Beach earthquake. Fortunately, theearthquake occurred after school hours, and a catastrophic loss of life was averted. However,the destruction was so extensive and had such dire consequences that the California legisla-ture passed the Field Law on April 10, 1933. This law required that all new public schoolsbe constructed so that they are highly resistant to earthquakes. The Field Law also requiredthat there be field supervision during the construction of schools.

2. February 9, 1971, San Fernando earthquake in California: Because of the dam-age caused by this earthquake, building codes were strengthened, and the California legis-lature passed the Alquist Priolo Special Studies Zone Act in 1972. The purpose of this actis to prohibit the construction of structures for human occupancy across the traces of active

faults. The goal of this legislation is to mitigate the hazards caused by fault rupture.There has also been a considerable amount of federal legislation in response to earth-

quake damage. For example, the Federal Emergency Management Agency (1994) states:

At the federal level, there are two important pieces of legislation relating to local seismichazard assessment. These are Public Law 93-288, amended in 1988 as the Stafford Act, whichestablishes basic rules for federal disaster assistance and relief, and the Earthquake HazardsReduction Act of 1977, amended in 1990, which establishes the National Earthquake HazardsReduction Program (NEHRP).

The Stafford Act briefly mentions “construction and land use” as possible mitigation mea-sures to be used after a disaster to forestall repetition of damage and destruction in subsequentevents. However, the final rules promulgated by the Federal Emergency Management Agency(FEMA) to implement the Stafford Act (44 CFR Part 206, Subparts M and N) require post-dis-aster state-local hazard mitigation plans to be prepared as a prerequisite for local governmentsto receive disaster assistance funds to repair and restore damaged or destroyed public facilities.Under the regulations implementing Sec. 409 of the Stafford Act, a city or county must adopta hazard mitigation plan acceptable to FEMA if it is to receive facilities restoration assistanceauthorized under Sec. 406.

The overall purpose of the National Earthquake Hazards Reduction Act is to reduce risks

to life and property from earthquakes. This is to be carried out through activities such as: haz-ard identification and vulnerability studies; development and dissemination of seismic designand construction standards; development of an earthquake prediction capability; preparation of national, state, and local plans for mitigation, preparedness, and response; conduct basic andapplied research into causes and implications of earthquake hazards; and, education of the pub-lic about earthquakes. While this bears less directly on earthquake preparation for a particularlocal government, much of the growing body of earthquake-related scientific and engineeringknowledge has been developed through NEHRP funded research, including this study.

14.3 LIMITATIONS OF BUILDING CODES

Common limitations of building codes are that they may not be up to date or may underes-timate the potential for earthquake shaking at a particular area. In addition, the buildingcodes may not be technically sound, or they may contain loopholes that can be exploitedby developers. For example, in terms of the collapse of structures caused by the Chi-chiearthquake in Taiwan on September 21, 1999, Hands (1999) states:

Why then were so many of these collapses occurring in 12-story buildings? Was it, as the

local media suggested, a result of seismic waves hitting just the right resonant frequency to take

14.4 CHAPTER FOURTEEN

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them out? Professor Chern dismisses this as bordering on superstition. “Basically Taiwan hasa lot of 12-story buildings, especially central Taiwan. You hardly see any 20-story high-risesin those areas hit by the quake. The reason for this is that buildings under 50 meters in heightdon’t have to go to a special engineering committee to be approved, so 12 stories is just right.”Approval of a structure by qualified structural engineers, and correct enforcement of the build-

ing codes, is the crux of the problem, Chern believes.

Another example is the Kobe earthquake in Japan on January 17, 1995. It was observedthat a large number of 20-year-old and older high-rise buildings collapsed at the fifth floor.The cause of these building collapses was apparently an older version of the building codethat allowed a weaker superstructure beginning at the fifth floor.

Even with a technically sound building code without loopholes, there could be manyother factors that are needed to produce earthquake-resistant structures:

1. Qualified engineers: There must be qualified structural and geotechnical engineerswho can prepare seismic designs and building plans. However, the availability of a profes-sional engineering group will not ensure adequate designs. For example, concerning thecollapse of structures caused by the Chi-chi earthquake in Taiwan on September 21, 1999,Hands (1999) states:

Professor Chern is particularly damning of some of his fellow engineers, and the profes-sional associations to which they belong. “In 1997 we had 6,300 registered civil engineers.Three hundred of them are working in their own consultancies, and 2,800 are employed by

building contractors. That means that the other 3,300, or more than half, are possibly rentingtheir licenses.” Asked to explain further, Chern said that it was common practice for an engi-neer to rent his engineer’s license to a building contractor, so that the contractor could thenclaim the architectural drawings had been approved by a qualified engineer, without the engi-neer even having seen the blueprints. Chern sees the problem as stemming from the way theengineers’ professional associations are run. “When they elect a president of the association,the candidate who favors license-renting will get all the votes from those people and win theelection, and then he won’t be willing to do anything about the problem.”

2. Permit process: After the engineers have prepared the structural plans and specifi-cations, the plans must be reviewed and approved by the governing agency. The local juris-diction should have qualified engineers who review the designs to ensure that properactions are taken to mitigate the impact of seismic hazards, to evaluate structural and non-structural seismic design and construction practices so that they minimize earthquake dam-age in critical facilities, and to prevent the total collapse of any structure designed forhuman occupancy. An important aspect of the permit process is that the governing agencyhas the power to deny construction of the project if it is deemed to be below the standardof practice.

3. Inspection during construction: Similar to the permit process, there must be ade-quate inspection during the construction of the project to ensure that the approved buildingplans and specifications are being followed. Any proposed changes to the approved build-ing plans and specifications would have to be reviewed by the governing agency. The pro-

ject engineers should issue final reports to certify that the structure was built inconformance with the approved building plans.

4. Construction industry: An experienced workforce that will follow the approvedplans and specifications is needed during construction. In addition, there must be availablematerials that meet project requirements in terms of quality, strength, etc. An example of

lax construction follows (Hands 1999):

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Professor Chern said the construction industry is riddled with problems from top to bottom.Even the concrete has problems. “In Taiwan we have quite narrow columns with a lot of rebarin them. This makes it difficult to pour the concrete and get it through and into all the spacesbetween the bars. Just imagine it—you usually have a small contractor doing the pouring,maybe five men with one pumping car, with two doing the vibrating. They pour 400 cubic

meters in one day, and only make NT$5,000 for one morning’s work.”It’s also a manpower quality problem, he said. “You have low quality workers on low pay,

so everything is done quickly. Very good concrete is viscous, so they add water to ready-mixedconcrete to make it flow better. But then you get segregation of the cement and aggregate, andthe bonding of the concrete and rebar is poor. We’ve seen that in a lot of the collapsed build-ings. Adding water is the usual practice,” Chern said. “They even bring along a water tank forthe purpose.” And although structural engineers are wont to criticize architects for designingpretty buildings that fall down in quakes, perhaps the opposite extreme should also be avoided.“If I had my way all buildings would be squat concrete cubes with no windows,” joked VincentBorov, an engineer with the EQE team.

14.6 CHAPTER FOURTEEN

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