Editor' Note

The February 2005 issue of the Practice Periodical on Structural Design and Construction contains eight interesting and practical papers in addition to the structural design and construction forums.

The first paper is entitled “Comparative Study of Optimum Design of Steel Highrise Building Structures Using ASD and LRFD Codes” and was prepared by K. C. Sarma and H. Adeli. The writers created an optimization model for automated design of large steel structures subject to actual constraints of commonly used design codes. In this work the optimization model is used to perform a comparative study of optimum designs of steel highrise buildings using AISC ASC and LRFD codes. The paper presents results for two large structures, a 36-story moment-resisting frame and a 144-story super high-rise building. The use of the LRFD code results in the cost savings in the range of 3.0–6.9% for the 36-story building and 1.7–4.3% for the 144-story building. When serviceability (stiffness) is more of a controlling factor, the LRFD code in general yields a much smaller advantage for weight savings.

The second paper in this issue is entitled “Analysis of Horizontally Curved Bridges Using Simple Finite-Element Models” and was prepared by E. DeSantiago, J. Mohammadi, and H. M. O. Albaijat, all of the Illinois Institute of Technology, Chicago. In the study reported, a series of horizontally curved bridges were analyzed using simple finite-element models. These were single-span bridges having a horizontal angle of curvature in the range from $20–30\text{degrees}$ . The spans were about $30.5\mathrm{m}$ $\left(100\mathrm{ft}\right)$ with the chord length being $30.5\mathrm{m}$ $\left(100\mathrm{ft}\right)$ for all bridges. The bridges consisted of steel beams, diaphragms, and an $203\mathrm{mm}$ $\left(8\mathrm{in.}\right)$ reinforced concrete slab. The loading consisted of standard AASHTO trucks plus dead load. The finite-element models made use of simple beam elements for top and bottom flanges and plate bending elements for girder webs and the slab. The results showed that the bending moment in a curved bridge can be about 23.5% higher when compared to straight bridges of similar span and loading. As the result of curved geometry a torsional moment is developed in the girders. The magnitude of this moment was found to be about 10.3% of the maximum bending moment in a comparable straight bridge.

“Static Soil–Structure Interaction Effects in Seismically Isolated Bridges” is a paper prepared by M. Dicleli and S. Albhaisi of Bradley University, Peoria, Ill., and M. Y. Mansour of the University of British Columbia, Canada. In this study, two seismically isolated bridges were analyzed. The bridges are representative of two categories—bridges with heavy superstructure and light substructure and bridges with light superstructure and heavy substructure. Detailed structural models of both bridges, excluding and including soil–structure interaction, were first constructed. Iterative multimode response spectrum analyses of the bridges were then conducted considering nonlinear behavior of isolation bearings. Results show that soil–structure interaction, effects may be neglected in seismic analysis of seismically iso-lated bridges with heavy superstructure and light substructure constructed in stiff soil. However, soil–structure interaction effects need to be considered in bridges with light superstructures regardless of the stiffness of the foundation soil. In soft soils, soil–structure interaction needs to be considered regardless of bridge type.

Interesting and practical results are reported in the paper entitled “Uniform Serviceability Load Limits for Mechanical Flange Connectors” prepared by J. W. van de Lindt and H. A. de Melo e Silva, both of Michigan Tech, Houghton, Mich. This paper deals with parking garages in which floors and roofs consist of T-beams whose flanges are connected with mechanical flange connectors. Cracking of concrete around these flange connectors is a common problem requiring significant labor hours for repair and maintenance. Suggested design load levels—which in the opinion of the authors may significantly reduce the cracking of these structures—are presented. This opinion is based on the results of 49 monotonic displacement control tests performed on six different types of commercially available flange connectors embedded in concrete slabs. The slabs were designed to be representative of the flange of a typical precast concrete double T-beam. Three different types of monotonic tests were performed: horizontal shear, vertical shear, and tension. Basic statistics were used to analyze the data. Final results were grouped into four regions—cracking unlikely, cracking possible, cracking likely, and cracking probable.

Another informative paper dealing with reinforced concrete (RC) is entitled “In-Situ Load Testing of Parking Garage Reinforced Concrete Slabs: Comparison between $24-\text{Hour}$ and Cyclic Load Testing.” It was prepared by P. Casadei, R. Parretti, and A. Nanni of Rolla, Mo., and T. Heinze of Clayton, Mo. This paper reports on the results obtained on the applicability of the diagnostic cyclic-load test method in comparison with the existing $24-\mathrm{h}$ test procedure adopted in ACI-318. A parking garage scheduled for demolition was used as a research bed before demolition. This structure, a two-story steel and reinforced concrete frame with one-way RC slabs built in 1970s, was ideal in terms of size and construction system for performing comparative field experiments on load testing. Two identical RC slabs were tested, both according to the standard procedure (ACI-318-02 2002) and the proposed diagnostic load testing (CIAS Report 00-1 2001). In both instances the applied total load was such that the slab did not pass the load test. This allowed characterizing the critical test parameters that govern acceptability and draw conclusions on their values. After load testing, both slabs were loaded until partial collapse was reached. This allowed for making observations on the margin of safety with respect to collapse, a determination that is not generally possible in a proof test. The results of the tests provide professionals with evidence on the validity of in-situ assessment for the adequacy of structural members.

A paper that should be of interest to earthquake engineers dealing with historic structures is entitled “Earthquake-Resistant Design and Rehabilitation of Masonry Historical Structures.” It was prepared by P. G. Asteris and A. D. Tzamtzis of the Technological Educational Institution of Athens, Greece, and P. P. Vouthouni of Aristotle University of Thessaloniki, Greece. In this paper a general methodology for earthquake-resistant design and rehabilitation of damaged masonry structures is presented. The process is illustrated by means of a case study—the rehabilitation of Zoodohos Pigi Holy Temple in Athens, a structure that suffered extensive damage during the September 1999 Athens earthquake. The procedures followed in the design, together with a description of the actions taken for the rehabilitation of the temple and it’s strengthening against future earthquake actions are reported.

“Quincha Construction in Peru” is a paper prepared by F. Carbajal and G. Ruiz of Piura, Peru, and C. J. Schexnayder of Arizona State University. Because lack of housing and the high cost of construction are problems faced by all nations, the authors contend that a viable solution to the lack of housing in many parts of the world may be found in traditional earthen construction methods. In Peru, ancestral building methods such adobe, tapial, and quincha take advantage of local resources for housing construction. These methods have been used for centuries and do not require commercially processed materials or a skilled labor force. Unskilled local labor can satisfactorily construct a house using these methods. This paper presents a description of the quincha construction methods as practiced in Peru.

“Use of Rock Blocks to Protect the Downstream Zone of a Hydraulic Discharge Structure” is a paper prepared by S. R. Vegas Merino and J. R. Salazar of Piura, Peru, and C. J. Schexnayder of Arizona State University. Water discharged from a hydraulic retention structure can cause erosion in the zone immediately downstream and adjacent to the structure. Special erosion protection is necessary in the downstream discharge zone of retention structures. Protection that has given satisfactory results in Peru is the use of block pavements. Blocks effectively form a plate to resist the impact and abrasive action of discharge flow. This paper details the construction process of one particular hydraulic structure that used rock blocks for erosion protection. Blocks were installed after the structure had experienced significant erosion of the stilling basin below its inflatable dam.

Readers are invited to comment on any of these papers by means of discussions.