Practice Periodical on Structural Design and Construction

Axial shortening of columns due to long term creep and shrinkage is inevitable in tall reinforced concrete buildings. However, calculation of exact values of axial shortening is not a straight forward task since it depends on a number of parameters such as the type of concrete, reinforcement ratio, and the rate and sequence of construction. All these parameters may or may not be available to the design engineer at the preliminary design stage of construction. Furthermore, long term shortening of columns could affect the horizontal structural members such as beams and floors and hence could affect the finishes and partitions. Therefore, a reasonable idea about the probable axial shortening could be important for construction engineers and project managers as well. In this study, the effects of construction sequence, rate of construction, and grade of concrete on axial shortening are determined based on a number of case studies covering 10–40 story range. These are presented as a set of guidelines so that the effect could be taken into account approximately, especially at the preliminary design stage and also during the construction phase.

The 50-story One Shell Plaza Building, when completed in 1971, was the tallest concrete building in the world. Towering at 217.7 m (714 ft), One Shell Plaza still reigns as the tallest lightweight concrete building in the world. Design and construction issues are presented for tall building purposes.

There are several changes in the American Concrete Institute’s 318-02 building code from 1999 that have had a significant impact upon beam analysis and design. On one side of the equation, the load factors are now based on ASCE 7-98 combinations. On the other side of the equation, strength reduction factors were “adjusted to be compatible with ASCE 7-98.” Concrete sections are now classified as either tension controlled or compression controlled with a transition region between. For beams with little or no axial force, there is a limit on strain in the tension steel that replaces the previous limit resulting from a maximum allowable tension of 75% balanced. This new strain limit has some interesting ramifications for the design of new beams or the capacity of existing beams that structural engineers will need to know. There are clarifications that will probably eventually be part of the 318-02 commentary or will appear in future reinforced-concrete texts. This paper shows, through several numerical examples, how the new strain provision may affect capacity.

An area of heightened interest after the 1994 Northridge earthquake damage was the seismic ductility of steel moment frame connections. Work conducted by the Federal Emergency Management Agency (FEMA) and the SAC Joint Venture, National Institute of Standards and Technology (NIST), the American Institute of Steel Construction Inc. (AISC), and many others in academia, industry, and the profession over the last few years has greatly expanded the knowledge base in a number of relevant areas. This resulting information has led to a set of new and modified steel moment connection details and accompanying design criteria for improved seismic performance. One of the more popular seismic connection types that has been prequalified in FEMA 350–353 is the new reduced beam section detail.

A new approach and tables developed for design of steel beam-columns are presented. The new method, which was adopted by the American Institute of Steel Construction (AISC) and has been included in the third edition of the AISC-LRFD Manual of Steel Construction, is an exact, fast, and rational method for effective design of members subjected to combined axial and bending stresses. Numerical example problems are presented to illustrate effective use of the method and tables. Tables developed cover a wide range of W-sections; however, the general approach applies to all sections. Further, the load and resistance factor design (LRFD) method is used in all discussions and examples presented, but the concepts apply equally to design of beam-columns based on the allowable stress design (ASD) method as well.

Pole building construction has gained popularity in the Midwestern United States due to its low cost and rapid construction applications. Farm and agricultural buildings, low-rise commercial units, and some storage facilities have utilized this type of construction technique. This paper reviews some common features of pole buildings and presents a case study for stricter construction supervision by design professionals, contractors, and building officials, alike.

On the Arizona Department of Transportation U.S. 60 Superstition Freeway project it was necessary to construct a new mainline bridge-widening superstructure at an elevation above its final position. This was done so that the required concrete formwork would not cause a decrease in clearance on the road passing under the existing bridge. The focus of this paper is the planning and execution of jacking the constructed bridge sections into their final positions. An unusual inverted jack system was used to accomplish this lowering operation.

Harmful vibration effects of construction operations occur frequently. Ground vibrations may affect adjacent and remote structures. The level of structure vibrations depends on a number of factors such as characterized sources of vibrations, soil conditions, and susceptibility of structures. There is no unique solution to minimize the effects of construction vibrations at every site. Monitoring and control of construction vibrations are made to be in compliance with safe vibration criteria. Reasonable vibration criteria should be chosen for a site.

The need for utility service line replacement or repairs with minimum disruption to the surface has increased the demand for trenchless excavation methods like microtunneling. Microtunneling is a trenchless technique that is used in installation of new pipelines. Microtunneling can be applied in gravity and pressure lines, permanent ducts for cables, and crossings under rails or roads. In order to give a better view of the microtunneling method, a successful case study of a microtunneling project is presented. This project was one of the projects to construct a new sewer system supplementary to the old sewer system in Cairo, Egypt. Boulac is a very crowded district of Cairo, Egypt, with about 4 million people. The contractor was a consortium of five specialized international companies. The engineer was a consortium of four American and British companies. Boulac’s microtunneling project value was about $300 million and lasted for about 5 years. The length of microtunneling drives in Boulac was about 6.0 km. Microtunneling machines of 600 and 1,000 mm diameters were used. The productivity of the machines has been analyzed including consideration of factors such as the operator’s experience in different soils for different microtunneling machines.