photoelastic analysis of cracked frames with lose of support

6.1 This research is concerned with studying the behavior of multi-story frame containing cracks at loss of soil support tacking into consideration the soil-structure interaction problem is solved by using experimental and numerical technique.In the experimental technique, a model was developed which simulate the actual frame-soil conditions by using two different photoelastic materials and constraint the soil part by test plate normal to the surface was achieved to simulate plain strain conditions existing in practical situations.In the numerical analysis a computer program based on finite element technique is developed to solve the multi-story frame-soil plain stress-strain problem.The experimental and numerical techniques are used to study the different parameters on the behavior of frame and soil stresses.The considered parameters are the horizontal and vertical dimensions of loss of soil support, the size and location of cracks, case of loading and location of tie beam.Distribution of internal forces on frame and stresses of soil have been obtained using both experimental and numerical technique.A comparison has been made between experimental and numerical results to prove the accuracy of the introduced numerical technique.6.2 CONLUSIONSThe most important conclusions can be summarized as follow:1- The increase of the horizontal length of loss of soil support at certain limit tends to increase the redistribution of the frame internal forces and soil stress. However the increases of the vertical height of loss of soil support has a slight effect.2- The presence of cracks in multi-story frames produces stress concentration in the soil under the frame and decreases the bending moment in cracked section and increase the bending moment on some other sections of frame, this change in values of binding moment ranges from 5 to 35% according to crack-depth ratio.3- The maximum possible safe of horizontal length of loss of soil support of frame not contain cracks is about 1.5 as much that of frame contains cracks.4- Frame with tie beam between footings can stabilize more in cracks location and depth; however frame with tie beam upper footings fail with less crack- depth and number with the increase of the horizontal length of loss of soil support.5- Lateral displacement increase with the increase of loss of soil support ratios  and more increased at ratio of loss of soil support =0.40 up to 4 times for it at ratio 0.24.6- The presence of cracks in the frame with loss of support produces an increase in the maximum lateral displacement about 0.05%, especially in frame with tie beam upper footings it reach the double in some cases.7- The increase of the horizontal length of loss of soil support increases the soil stress beside the gape. The average rate of this increment is about 20% for each ratio of loss of support.8- The maximum safe horizontal length of loss of soil support affected by case of loading which decrease in case of lateral load to reach 50% than in case of vertical load.9- The tie beam between footings increase the safety of frame than the tie upper footings where the maximum safe horizontal length of loss of soil support for frame with tie beam between footings about 2 times of it with tie upper footings.10- The numerical results are compared with the experimental, and good agreement is observed. The difference between experimental and numerical results was about 5 to 15% in some cases.RECOMMENDATIONS FOR FURTHER WORKIt is recommended to concentrate in further work on the following:1- Analysis of frame due to dynamic load.2- Analysis of frame in non linear analysis3- Analysis of infield frame with loss of support.