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The building defects are always of great concern for construction industry as they cause delays before handing over and increase maintenance costs during occupancy of the buildings. Due to the rapid development and population growth in Gaza Strip, many residential buildings and housing projects are being constructed in a short space of time, especially after Gaza war in 2014. Therefore, many errors and defects are expected to arise during the construction stage. The aim of this paper is to identify and rank the factors affecting the defects occurrence in the construction stage of the residential buildings in Gaza Strip. A survey was conducted in 134 randomly selected engineers working for engineering offices as design engineers, supervisors and project managers in Gaza Strip. The study revealed five most effective main factors during the construction stage, namely construction materials, factors due to inspections, factors due to construction equipment, factors due to constructions and factors due to construction management, respectively. The most important factors in each group were poor soil compaction, exceeding the allowable limits of verticality of the structural elements, insufficient reinforcement concrete cover, owner's negligence of inspections, absence of engineer in most of construction phases, using expired material, material or component failure, using corroded or secondhand reinforcement steel, using materials not of acceptable quality and not conforming to the specifications or design and lack of required equipment. This research is the first attempt at identifying factors affecting defect occurrence in the construction stage of residential buildings of the developing countries. The findings will be useful for the construction firms and regulatory bodies to deal with the critical factors affecting defect occurrence and device such policies that improve the design and construction of residential buildings.

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Cement production involves high amounts of energy consumption and carbon dioxide emissions. Pakistan is facing a serious energy crisis and cement’s cost is increasing. In addition, landfilling of potential concrete components can lead to environmental degradation. The use of waste as cement replacement not only reduces cement production cost by reducing energy consumption, but it is also environmentally friendly. The purpose of this study is to analyze the characteristics of concrete by partially replacing cement with Rice Husk Ash (RHA) and Fly Ash (FA). This study is mainly focused on the performance of concrete conducting a slump test, and investigating indirect tensile and compressive strength. Cement was replaced with RHA and FA by 5% (2.5% RHA + 2.5% FA), 10% (5% RHA + 5% FA), 15% (7.5% RHA + 7.5% FA) and 20% (10% RHA+10% FA) by weight. Ninety concrete samples were cast with mix proportions of 1:2:4 and 0.55 water/cement ratio. Cube and cylindrical samples were used for measuring compressive and split tensile strength respectively, after 7 and 28 days. The results showed that after 28 days, the 5% RHA+5% FA sample’s compressive strength was enhanced by 16.14% and its indirect tensile strength was improved by 15.20% compared to the conventional sample. Moreover, the sample’s slump value dropped as the content of RHA and FA increased.

The seismic response of the high-rise reinforced concrete (RC) wall structures is really complicated as several vibration modes other than the fundamental mode normally contribute significantly to the response-commonly recognized as 'higher mode effects'. Response spectrum analysis (RSA) procedure, which can account for higher mode effects, is usually employed to compute the seismic design demand for the high-rise structures. Recent studies show that the inelastic seismic force demands obtained from the rigorous nonlinear response history analysis procedure are much larger than the seismic force design demands obtained from the code-based RSA procedure for the high-rise RC wall structures. Though, the nonlinear response history analysis procedure is widely accepted for its ability to provide the most accurate estimate of nonlinear seismic responses, the obtained responses are generally so complex that it is quite difficult for engineers to grasp the overall picture of the responses and gain some insight into them and use them to understand the cause of high seismic demands. Another important issue related to the nonlinear seismic response prediction of the high-rise RC wall structures is the realistic and accurate numerical modeling of RC walls. In this study, a simplified but reasonably accurate procedure called the uncoupled modal response history analysis procedure is used to interpret the complex nonlinear behavior of high-rise RC wall structures. Moreover, a finite element model based on modified compression field theory is employed for accurate numerical modeling of RC walls by incorporating the axial-flexure-shear interaction. This study, by making use of a better computer modeling approach and an in-depth analysis by modal decomposition, aims to resolve some of the unanswered questions regarding realistic prediction of nonlinear seismic demands of high-rise structures. KEYWORDS finite element modeling, higher modes, high-rise, modal decomposition, RC core wall buildings, uncoupled modal response history analysis procedure