INVESTIGATION OF BUCKING RESTRAINED BRACED FRAMES (BRBF) FOR CONSTRUCTION AND RETROFIT OF LOW-RISE BUILDINGS IN IRAN

Lack of lateral resistance of many old buildings in Iran has resulted in their severe damage during the past earthquakes. Such buildings are being replaced by new and, supposedly, improved designs. However, damage to the new buildings in the subsequent quakes has been an indication that the improvements have not been satisfactory. It is obvious that a serious effort during the redesign of damaged structures, taking advantage of the advanced design and construction methodologies, goes a long way in enhancing the safety of inhabitants and in restoring their faith in the engineering profession. Following the great tragedy of Bam additional efforts have been made in rebuilding the community in a safe way. To effect a minimum degree of safety and quality control, a set of ten plans have been put forward by consulting engineering firms that were selected by the Iranian office of Management and Planning Organization. Each family attempting to rebuild its home will have to choose from those plans, the construction of which will have to be supervised by one of the selected firms. Here we consider only one of the plans that use regular braced frames in masonry walls. These frames will be the main resistance mechanism against lateral loads of earthquake. Obviously this is a great improvement over the old unengineered unreinforced masonry buildings. Steel braces of this type have been used as an economical means of providing lateral stiffness to steel structures and can have a place in other types of structure as well. However, the energy dissipation capacity of steel braces subjected to earthquake forces is limited because of buckling of the brace element in compression. The energy dissipation, i.e. the damage prevention capacity can be greatly enhanced by employing bucking restrained braces (BRBs). In view of the high degree of vulnerability of most areas in Iran such improvement is highly desirable, even if it comes at a small additional cost. The possibility of using BRBs in Iran hinges on the ability to produce them locally. The present system patented in Japan has a high cost, because of the patent, and long delivery time. A parallel study is investigating alternatives to the Japanese system to be constructed with the still available in Iran. The purpose of the present study was therefore to investigate the application of BRBs as an improved system of resisting lateral forces, i.e. as a replacement for regular braces. Although at present some 1300 systems with regular braced frames have been used in the reconstruction project of Bam, it may still be time to employ the new system for the projects that are at planning stage. Once proved effective and economical for use in Iran, because no new technology is needed for its application it can be used in many parts of the country. The first part of the project was the use of performance based procedures to compare the capacity of the regular braced frames to that of BRBs. In addition to cost comparisons, the advantages and disadvantages of the systems will be highlighted and the load and displacement capacities, as well as the ductility of the two systems will be determined up to collapse of the structure. Because of the small physical difference from standard braces, but the major improvement in the behavior, BRBs may prove to be an effective system for low rise buildings in Iran.