The expansion of an entertainment complex in the eastern US was under construction in 2003 when a portion of a multi-story parking garage collapsed during an 8th level concrete floor pour. This investigation was initiated to determine the cause of progressive collapse. Garage construction generally consisted of stay-in-place, precast, prestressed concrete formwork and cast-in-place composite floor system connected with mild steel reinforcing to cast-in-place concrete columns and shear walls. The collapse of an approximate 50 by 180 ft. area of the garage occurred during placement of cast-in-place floor system concrete at an upper level of the parking garage. A progressive failure of multiple levels of the stay-in-place precast formwork and cast-in-place composite floor system occurred, but nearly all perimeter columns and shear walls in the area remained standing. The authors were retained to investigate and evaluate the cause of the failure and study the progressive collapse. The investigation included site inspections of the garage collapse site and examination of garage structural components at an off-site location where debris was retained following demolition efforts. Visual inspection of the debris, review of eyewitness accounts, examination of construction documents, and structural analyses were used to evaluate the cause of the progressive collapse. Hand calculations and a three dimensional non-linear fracture mechanics model were also used to assess structural behavior of the composite reinforced concrete garage system. Strength of as-designed and influence of as-constructed connection conditions between the precast formwork floor system and cast-in-place columns and shear walls were evaluated. Results of the investigation were used to successfully assess the cause of the failure and make recommendations on how to avoid such accidents in the future.

The “Building Code Requirements for Structural Concrete” (“Code”) covers the materials, design, and construction of structural concrete used in buildings and where applicable in nonbuilding structures. The Code also covers the strength evaluation of existing concrete structures. Among the subjects covered are: contract documents; inspection; materials; durability requirements; concrete quality, mixing, and placing; formwork; embedded pipes; construction joints; reinforcement details; analysis and design; strength and serviceability; flexural and axial loads; shear and torsion; development and splices of reinforcement; slab systems; walls; footings; precast concrete; composite flexural members; prestressed concrete; shells and folded plate members; strength evaluation of existing structures; provisions for seismic design; structural plain concrete; strut-and-tie modeling in Appendix A; alternative design provisions in Appendix B; alternative load and strength reduction factors in Appendix C; and anchoring to concrete in Appendix D. The quality and testing of materials used in construction are covered by reference to the appropriate ASTM standard specifications. Welding of reinforcement is covered by reference to the appropriate American Welding Society (AWS) standard. Uses of the Code include adoption by reference in general building codes, and earlier editions have been widely used in this manner. The Code is written in a format that allows such reference without change to its language. Therefore, background details or suggestions for carrying out the requirements or intent of the Code portion cannot be included. The Commentary is provided for this purpose. Some of the considerations of the committee in developing the Code portion are discussed within the Commentary, with emphasis given to the explanation of new or revised provisions. Much of the research data referenced in preparing the Code is cited for the user desiring to study individual questions in greater detail. Other documents that provide suggestions for carrying out the requirements of the Code are also cited.

Chapter 14 Blast-Resistant Design Concepts and Member Detailing: Concrete Steven Smith, Steven SmithSearch for more papers by this authorW. Gene Corley, W. Gene CorleySearch for more papers by this author Steven Smith, Steven SmithSearch for more papers by this authorW. Gene Corley, W. Gene CorleySearch for more papers by this author Book Editor(s):Donald O. Dusenberry, Donald O. DusenberrySearch for more papers by this author First published: 06 January 2010 https://doi.org/10.1002/9780470549070.ch14 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: General Failure Modes Detailing Handbook for Blast‐Resistant Design of Buildings RelatedInformation

This paper presents the work of the Blast Protection of Buildings Task Committees on Materials Detailing and Performance Verification. The paper covers the last two chapters of the Standard that deal with design and detailing of structural components constructed of steel, concrete, masonry and fiber-reinforced plastics (Chapter 9), and performance qualification of site perimeter components, structural and nonstructural components and shielding structures (Chapter 10). The materials chapter references existing US standards where applicable and identifies more stringent design and detailing requirements for blast effects as needed. Prescriptive detailing requirements are scaled according to four Levels of Protection (LOP). Each LOP, from I to IV, provides increasing blast resistance beyond the nominal resistance provided by conventional design methods. The chapter on performance qualification address issues related to verification of the performance characteristics of manufactured products by analysis and design, and peer review of blast-resistant designs and performance qualification.

Structural engineers design green buildings using the LEED™ Green Building Rating System™, a point-based system for certifying the level of a building’s sustainability. Structural materials play a large part in increasing a building’s sustainability. Using concrete, for example, can help in brownfield redevelopment, reduce urban heat islands, mitigate water runoff, help meet minimum energy requirements, optimize energy performance, and increase the life of a building. Concrete and its constituents are usually available locally. Both concrete and steel can be recycled. Steel, fabricated in a shop, creates little to no on-site waste and has high recycled content. Attributes of these structural materials, and others, along with decisions made by design professionals help to lessen the impact a structure has on the natural environment.

The expansion of a casino entertainment complex in the eastern United States was progressing in 2003, when a collapse of an approximate 15 by 60 m area of the parking garage occurred during placement of cast-in-place concrete at an upper garage level. Garage construction generally consisted of stay-in-place, precast, prestressed concrete formwork and cast-in-place composite slab system connected with mild steel reinforcing to cast-in-place concrete columns and shearwalls..Collapse of multiple levels of the composite floor system occurred, but nearly all perimeter columns and shearwalls in the area remained standing. The authors were retained to investigate and determine the cause of the failure and study the progressive collapse. The investigation results were used to successfully assess failure cause and make recommendations on how to avoid such accidents in the future.

Jon Schmidt represents the Structural Engineers Association of Kansas & Missouri (SEAKM), the sponsor of this session, as a member of its Professional Practice Committee. Ten states currently have specific provisions in place that distinguish structural engineers from professional engineers in other disciplines. However, there is considerable variation among these jurisdictions in the qualifications that are required for structural engineering (S.E.) licensure. There are also important differences in the significance of S.E. licensure within each jurisdiction. This inhibits the mobility of those who already have the S.E. license in one state and seek to obtain it in another. Recognizing this, NCEES added a definition for a Model Law Structural Engineer (MLSE) to its Model Law in 2003 and its Council Records Program in 2005. Separately, the Member Organizations of NCSEA voted in 2003 to establish an independent body, SECB, to administer a national board certification program for structural engineers. The MLSE and SECB criteria are intended eventually to serve as the basis for national uniformity in the qualifications required for S.E. licensure.

Some engineers suggest that current seismic design provisions, both for new buildings and for strengthened existing buildings, can improve resistance to blast loads and progressive collapse. However, there have been few attempts to quantify such improvement. To begin analyzing this possible relationship between seismic detailing and blast and progressive collapse resistance, the Federal Emergency Management Agency of the Department of Homeland Security sponsored a study at the U.S. Army Engineer Research and Development Center. The study was an analysis of the Alfred P. Murrah Federal Building, which was severely damaged in a 1995 terrorist attack. The building was first evaluated for seismic vulnerabilities as if it were located in a seismically active region. Three strengthening schemes were then designed for the vulnerabilities found during the evaluation: a pier-spandrel system and a new special concrete moment frame, both for the street face of the building, and a set of internal shear walls. In addition to these strengthening schemes, the original ordinary concrete moment frame on the street face of the building was redetailed to bring it into compliance with current building code provisions, without including a lateral load analysis. The three strengthening schemes and redetailed frame were then analyzed for their responses to the same explosion that occurred in 1995. Blast and corresponding progressive collapse analyses showed that the pier-spandrel and special moment frame schemes, as well as the redetailed original system, reduced the degree of direct blast-induced damage and subsequent progressive collapse, compared with the behavior of the original building. Internal shear walls, however, were not as effective in reducing the blast and progressive collapse damage. A key finding of the study was that strengthening the perimeter elements using current seismic detailing techniques improved the survivability of the building, while strengthening elements internal to the building envelope was not nearly as effective in reducing damage.

ACI 318-05 contains a new provision aimed at reducing the potential for punching shear failures at columns in two–way slabs located in regions of high seismic risk or in structures assigned to high seismic performance or design categories. The provision requires that slab-column connections in two-way slabs without beams, where the slabs are assumed not to contribute to the lateral resistance of the structure, shall be provided with slab shear reinforcement unless: (1) it is shown that punching will not occur under the design shear and the moment induced between slab and column at the design displacement; or (2) the design story drift does not does not exceed a limiting value that is a function of the ratio of the design shear to the nominal shear strength of the connection under gravity loading. The reason for this new provision is described along with recommendations as to how to calculate the lateral load stiffness of two-way slab structures in accordance with ACI Code 318-05 requirements. Also described is how to utilize the provisions of Sec. 11.12.6 (shear resulting from moment transfer to columns) and Sec. 13.5.3 (reinforcement requirements for moment transfer to columns and moment redistribution between columns) to determine if the first alternative can be satisfied. Finally, the relation between these provisions and those of Sec. 21.12.6 for intermediate moment frames consisting of two-way slabs without beams is discussed.

The International Organization for Standardization (ISO) is developing a new international standard for the design of structural concrete. This article describes the development process, especially concerning the American Concrete Institute's role. Since concrete is such a multipurpose material, its use should not be hampered by technical differences between standards used in different countries. It is estimated that world trade in the concrete industry will increase by 1 to 2% when the new standard is implemented.

Several sources have suggested that current seismic design provisions can improve blast and progressive collapse resistance. To examine this suggestion, the Federal Emergency Management Agency (FEMA) of the U.S. Department of Homeland Security (DHS) sponsored a study at the U.S. Army Engineer Research and Development Center (ERDC). The Alfred P. Murrah Federal Building, which was severely damaged in a 1995 bombing, was hypothetically strengthened for high seismic demands. Three strengthening schemes were designed, and each strengthening scheme was then analyzed for its response to the 1995 bombing scenario. The blast and corresponding progressive collapse analyses showed that the pierspandrel and special moment frame schemes would significantly reduce the amount of blast-induced damage and subsequent progressive collapse, compared with the response of the original building. The internal shear walls were less effective in reducing blast and progressive collapse damage. It was concluded that strengthening perimeter elements using current seismic detailing techniques improved the survivability of the building from blast loading.

An investigation of concrete exposed to sulfate soils is used to illustrate a methodology for the systematic study of the condition of concrete in service. Condition surveys of the site and tests of engineering properties of the concrete were supplemented by examination of concrete cores using the stereomicroscope, the optical microscope, the electron microscope, analysis by wet chemistry, thermal analysis, and X-ray diffraction. Step-by-step progression from large scale (tens of meters) to submicroscopic scales (tens of nanometers) gave continuity to detailed test methods. It also allowed for the selection of specimens appropriately representing the concrete as a whole, and ensured reliable interpretation of the results. In many cases, more than one test method provided the same or similar information. The writers believe the methodology employed will be of value to other investigators.

A methodology for the systematic study of the condition of concrete in structures is presented in this paper. Historical review of the site and the environment, condition surveys and tests of engineering properties of the concrete are complemented by examination of the concrete using the stereomicroscope, optical microscope, electron microscope, analysis by wet chemistry, thermal analysis, and X-ray diffraction. The step-by-step progression from large scale to submicroscopic scale allows for the selection of specimens that appropriately represent the concrete, gives context to the detailed test methods and ensures reliable interpretation of the results. The authors believe that the methodology employed will be of value to investigators.

For more than 100 years, licensing of construction industry design professionals has served well to protect the public. In combination with building codes, licensing laws have reduced the number of structural failures to a very low level. In recent years, work done by structural engineers across state borders has increased. Because licensing laws are currently enacted on a state-by-state basis, practice across state lines is becoming impeded unnecessarily. This is because adjacent states often enact laws that have small unimportant differences thereby impeded cross-border licensing and restraining trade. This paper provides a model that would further increase the protection of the public while eliminating current restraints of trade. Through use of Federal legislation regulating trade, it is proposed that a structural practice act be established. Those who qualify under this act would be able to practice structural engineering in all jurisdictions.

The Technical Council on Forensic Engineering created a Research Committee to identify research needs for constructed facilities that do not perform in accordance with established standards, to define research problems and assign priorities to them, and to develop effective means for implementing the results of research. In 1991, the Research Committee completed a national survey. The intent of the questionnaire used in this survey was to identify the research needs related to forensic engineering. This paper summarizes the results of that poll. It is evident that civil engineers vary considerably in their opinions about research needs within their respective fields. However, significant needs were identified for information related to historical data, corrosion, new materials, leakage, in situ monitoring, and construction flaws.