Comparison of confined masonry buildings and reinforced concrete frames with infills under seismic loading.

Abstract

The main advantage of masonry buildings is their high compressive strength. They are heat and fire resistant and will last for over 100 years. Masonry interacts with the frame to improve the lateral load carrying capacity of the structure. This report presents the findings of the performance of bare frames, infilled frames and confined masonry against a similar seismic loading. The performance of masonry structures in the past few earthquakes reveal that they are not much efficient in taking earthquake loads without damage (Brzev, 2007). Earthquake damage on a masonry structure can cause cracks on bearing walls, roof, floors, and even cause building tilt. There is lack of enough knowledge on the performance of confined masonry and alternatives under seismic actions. In order to assess the performance of the different types of masonry structures, a maximum likelihood earthquake was first calculated for Kampala region. Then the bare frame, the infilled frame, and confined masonry were modelled with similar properties and subjected to the seismic load using sap2000 v20 software. After analysis using sap2000 v20 software, values on displacements were obtained and the performance of the structures analyzed. The seismic coefficient method was used to calculate the seismic loading on the different models using a period of vibration of 0.24s. The base shears and respective horizontal seismic loads were obtained from the calculations. The models made were of an idealized six-story bare frame, infilled frame and confined masonry in Sap2000 v20 software. The calculated horizontal seismic loads were applied on the models and the analysis run. The bare frame was modelled using frame elements that were designed in sap2000 v20 software. The infill panels in the reinforced concrete frames with infills was modelled using the diagonal strut method, because the masonry infill acts as a diagonal strut under seismic loading. Confined masonry was modelled using the wide column model because confined masonry acts as a shear wall under seismic loading. After linear analysis, displacements were obtained as joint displacements from the table outputs of sap2000 v20 software. The corresponding inter-story deflections and inter-story drifts were calculated using the story displacements in MS Excel software. The base shears obtained after calculation were 1303.902kN for the bare frame, and 1896.485kN for confined masonry and reinforced concrete frames with infills. The maximum roof displacements were 0.034347m, 0.019759m, and 0.003820m for the bare frame, infilled frame, and confined masonry models respectively. The inter-story deflections and inter-story ratios were within the acceptable ranges for all models. This study showed that much as all the models withstood the seismic loads within the accepted ranges of deformation, confined masonry performed best under seismic loading followed by the reinforced concrete frames with infills, this was because of the interaction the masonry infills had with the reinforced concrete frame. Further research should be considered on confined masonry like the effect of more than six stories, the effect of a soft story, and nonlinear analysis. This will bring more knowledge on confined masonry as an alternative under seismic loading.