Constructing an Innovative Base-Isolation System under Masonry Structures

Seismic up-gradation of existing buildings is a very challenging task, as it requires us to consider historical and economical aspects of building. While proposing a seismic-retrofit scheme for a historical building, one should keep in mind that it should be compatible with existing materials, be least intrusive, monitorable and removable. A novel base-isolation technique has been proposed for the up-gradation of existing buildings against seismic actions which does not involve any alteration in existing buildings, and it is monitorable and removable. The method asks for the uncoupling of soil under, and around the building, with the help of closely spaced microtunnels, trenches and retaining walls. Closely spaced microtunnels will lay under the foundation of building, running parallel to one of the dimension of the building, and base-isolation devices will be fitted in lining of these microtunnels. These closely spaced micro-tunnels, along with the trenches and retaining walls around the building, will isolate the structure from seismic actions. This assembly of microtunnels, fitted with isolation devices, and trenches, around the building, will be able to filter seismic forces in both directions of building. The construction of these micro-tunnels, for realisation of innovative base-isolation technique, is the most critical phase, because it can have a detrimental effect on building. This work explores the potential applicability of the novel base-isolation method on masonry buildings by assessing susceptibility of masonry wall, having different physical and material characteristics, to damage (relating to aesthetic of building) inflicted by the construction of microtunnels in various soil conditions. The effect of transverse ground movements is considered in this study. A parametric study is conducted using 2-D (coupled) nonlinear finite element analyses, considering factors such as strength and stiffness of masonry, stiffness of soil, soil-structure interface, excavation sequence of tunnels, different physical characteristics of wall and depth of tunnels. The study shows the applicability of innovative base-isolation technique, highlights the vulnerability levels of walls of different physical characteristics, emphasizes the importance of excavation sequence of microtunnels in reducing risk of damage, and mentions symptoms that correlate with damage

Experimental and Numerical Seismic Evaluation of RC Walls Under Axial Compression

Recent studies show that code-based equations usually do not provide an accurate estimate for the shear strength of short reinforced concrete (RC) walls due to the negligence of many important factors including the beneficial effect of axial compression. In the current study, quasi-static reversed cyclic testing is conducted for two RC wall specimens, one under axial load and one without axial load to assess the effect of the axial compression on the shear strength of RC walls in high-rise buildings. The results of the experimental study show that the axial compression load significantly improves the shear strength of RC walls. Results are also compared with the performance-based seismic evaluation code practices. Based on the experimental findings, recommendations are made for improvements in the existing codes. The experimental results are further compared with different numerical models to explore the suitable computer modeling options for non-linear response prediction of RC walls

Intrinsic psychosocial stressors and construction worker productivity: impact of employee age and industry experience

This paper aims to study the impact of employee age and industrial experience on intrinsic psychosocial stressors of construction workers. Using an integrated theoretical approach, this study examines the intrinsic (top management, career development, social support, motivation and work stress) psychosocial stressors that influence the productivity of Pakistani construction contracting firms workers having varied ages and industry experiences. Data were collected through a postal questionnaire survey. A comparative analysis of these data was undertaken for employees of varied ages and industrial experiences. Findings show that employees of varied ages did not concur over several top management, career development, social support, motivation and work stress related psychosocial stressors, whereas employees of varied industrial experience were in disagreement over some work stress related psychosocial stressors. Due to the need to overcome intrinsic psychological stresses, firm support is direly needed, especially for the less-experienced employees that are more susceptible to demotivation, mental stress and health and safety risks at the sites. The study provides valuable insights into worker productivity by showing how employee varied age and diverse industry experience are associated with the intrinsic psychosocial stressors that influence worker productivity. This study will help regulatory bodies to deal with the critical psychosocial stressors and devise such policies that improve the worker productivity of their construction contracting firms