03-23-2010, 12:40 PM
In my second post on this topic (post #2), I estimated the load that a typical column (at the foundation level) carries at 1.05 x 66426.67 = 69748KN (including its own weight). This was based on direct multiplication of the load at a typical floor level with the estimated numbers of floors supported by the column; as such I multiplied the load of (the typical floor load) by (estmated number of floors above the foundation level) and arrived at a loading of 249.1 x 267 = 66426.67KN. Since this is a very tall building, efforts will be made to economize on the building materials coupled with the fact that the structure should be as light as possible (without compromising stability/rigidity), as to impose as little as possible load on the supporting structures particularly the foundation. Following this reasoning, light weight materials had to be used. These manifested in the form of fiber glass forms and panels (for the floors ) topped up with light weight aggregates for the floor slab.
Typical fiber glass forms/panels topped up with light weight aggregates for the floor slab has unit volume weight of 14 KN/M^3
So the design dead load for the floor work = 14 x 0.2 + 0.8 = 3.6 KN/M^2 (0.8 KN/M^2 = the weight of the light weight partitioning, the fittings etc). Thus the design dead load = 1.3 x 3.6 = 4.68KN/M^3
Due to the fact that it is most unlikely that all the loads (particularly the live load) will be imposed on the structure at the same time, the codes allowed for the reduction of the live loads following the procedures specified in the relevant codes. The BS 8110 allowed the reduction of the load in the proportion of 10% for any successive floor above the 2nd floor up to the maximum of 50% i.e. from the 6th floor upwards. Since this reduction could start from the second floor and comparing the total numbers of floors involved, this means practically that the live load for all the floors could be reduced by 50%. Following this reasoning, we have live load = 50% of 3 = 1.50KN/M^2, thus design live load = 1.50 x 1.50 = 2.25 KN/M^2. This implies that the reversed design vertical load/floor = 20.3 (4.68+ 2.25) = 145.9KN. Ratio of the reversed design load to that calculated before = 140.7/249.1 = 0.565 as such the reversed design load/column at the foundation level = 69748 x 0.565 = 39390.1KN. Compare the result with the actual load (of 37000 KN) as recorded on the foundation of the building (refer to the circled part of the image above). The difference between the estimated load (of 39390.1KN) and the load registered at the pile locations (of 37000 KN), though small and not outside the margin of error, could be accounted for. This is due to:-
· The density or concentration of pile/unit plan area of the buildings foundation as compared to the assumed column spacing used in my estimate.
· The fact that I was not using the actual loadings as to the actual structure in my estimate but was trying to make an independent estimate as could be done in the preliminary stage of any design.
· That I was conservative in my estimate as this is necessary as to consider a more critical condition than could be experienced in the actual structure.
Regards
Teddy