This study is concerned with developing a rational design procedure for use of ductile steel bracing for strengthening existing seismically “weak” RC slab-column building structures. A one-third scale, two-bay, two-story RC slab-column frame model was selected to represent existing seismically inadequate structures of its type. The design procedure, construction and test results of the steel bracing system for strengthening the RC frame are presented in this paper. The strengthened frame was subjected to a combination of gravity and cyclic lateral loads up to 2% overall frame drifts. The behavior of the strengthened frame improved dramatically over that of the bare RC frame. A maximum 2.75% drift in the first story was reached which is highly probable during severe earthquake motions.
Due to the increasing number of fire accidents that are able to leave behind great losses and complete collapse of structures, structural fire safety has become a major consideration in the design of high rise buildings. The aim of this research is to evaluate how certain factors can influence the critical time (fire resistance) of concrete encased dual Ishaped steel columns under fire loads using ABAQUS. The parameters that were considered are: the applied load level, stiffness of surrounding structure to column, section dimensions, concrete cover, and axial distance from concrete surface to longitudinal bars. In order to achieve the posted objective, numerical investigation using ABAQUS software was used. The analysis method considered is an alternative of Heat Transfer Method. This approximate method is based on dividing the section into layers at the location of experimentally recorded temperature-time histories and then linking load amplitude to its corresponding layer. In the study, twelve models were generated which belong to three types of sections subjected to high and low load levels, as well as, high and low surrounding stiffness. It was found that decreasing the load level and increasing the concrete cover have a big influence in increasing the critical time of the column. The effect of increasing the stiffness of the surrounding on reducing the critical time is insignificant and can be eliminated by designers. However, the effect of slenderness (section dimensions) on the restraining axial force requires further investigation.
All new buildings nowadays have to be designed and executed to overcome any imposed type of loading (lateral/vertical). On a universal scale, the stock of buildings built before 1980’s is believed to be many times more than the number of newer buildings in most urban cities. In Beirut, as an example, a large proportion of Reinforced Concrete (RC) structures were constructed in the absence of mandatory earthquake design requirements, and unquestionably recognized as the type of construction most vulnerable to earthquakes. The performed research focused on how to evaluate the status of old building and how to design and execute the convenient seismic strengthening schemes. A case study has been selected to implement the evaluation process and design proposals. Conventional seismic upgrading technique has been assessed like the addition of shear walls in addition to more innovative approach which is the installation of steel bracing system. The strengthening schemes proposed aimed to create an ideal harmonization of the technical, economic and social aspects of the issue in hand. Analysis of the three structural systems (existing, modified with shear walls and with bracing systems) has been performed using the ETABS software including static equivalent, dynamic and pushover analyses. The research sorted out with a comparison between the systems based on different structural criteria followed by general recommendations and suggestions.
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