I have recently investigated a two storey house near Marikina Fault line. This fault line, can generate magnitude 7.2 earthquake according to MMEIRS. As structural engineer, we are required to refer to NSCP in designing house for earthquake prone region like Philippines. I discovered upon looking at the as built drawings that the beam size is only 150 x 300mm. I was surprised how little the beam was. Luckily, upon looking at the analysis, this beam will not carry sufficient amount of earthquake and will mostly carry gravity load of slab weight and occupant weight. The slab thickness will also contribute to additional strength of the beam. However, I will not design beam like that in order to save money.
The columns or post is luckily satisying the code provision of minimum dimension. The main problem is the beams which are supposed to carry earthquake loads. The main beams are all sized 200mm width and the reinforcements are not sufficient. On this cases, a more tedious analysis of the structure is required like setting up rigid end offset manually in the software to reduce moment carried by the beam, live load reduction if applicable and also reducing super imposed dead weight according to actual condition.
I would like to suggest to clients and readers that they keep design callculations submitted by structural engineers so that in the future, everyone looking at the plan will have ready references on the assumptions made by the engineer on record. This is normally practiced in building construction. Unfortunately, this is often neglected in residential construction..
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