Increasing the Lateral Capacity of Timber Wall Panels using Inexpensive FRP Retrofitting Techniques

Abstract

Dhajji Dewari is a traditional non-engineered open construction technique. These traditional timber structures are mostly found in Northern mountainous parts of Pakistan and in places where availability of conventional building construction materials is limited or restricted, so people have to make use of the locally available materials like timber, stone and mud etc. for building construction as well. From the past research work done on Dhajji Dewari construction type it was found out that the construction type has adequate earthquake resistance qualities. Also, it has other prominent features like affordability, ability to tolerate lateral forces and it can be utilized using cheap relatively untrained labour. This thesis presents experimental work conducted on typical Dhajji Dewari wall samples in two phases and their in-plane lateral load response was evaluated. Five reduced scale wall samples were constructed, two of the five walls were used as reference walls in the 1st phase of testing, the walls were bolted to the floor first without any joint strengthening applied and tested under in-plane monotonic loading, from the tests it was found that main vertical and horizontal joints governed major wall properties like its load carrying capacity, its ductility, energy dissipation and the wall’s mode of failure. So, to strengthen these critical vertical and horizontal joints, in the 1st phase of testing, conventional strengthening techniques were used (bamboo, metal strips and gusset plates) and their response was evaluated. For the 2nd phase of testing since there was limited research done on the subject of retrofitting aspect of Dhajji Dewari Walls, Fiber Reinforced Polymers were used in two forms (wraps and strips) to retrofit and strengthened the wall samples which were damaged from the initial testing. CFRP was used without and in conjunction with the strengthening techniques used in the 1st phase of testing and the walls were tested and evaluated under in-plane monotonic loading again. From the test results it was noted that use of CFRP in conjunction with 1st phase strengthening techniques caused a sort of over-strengthening of the wall, the wall sample started to show bending due to torsion without significant increase in the load carrying capacity of the wall as compared to the cost of construction increase, this torsion effect was significantly lessened in the wall sample where both CFRP wraps and strips were used in conjunction with initial strengthening but causing further increase in construction cost. On the other hand, walls retrofitted and strengthened with only CFRP on critical joints showed significant increase load carrying capacity, energy dissipation and ductility as compared to previously tested samples.