The recent change of the seismic zone factor in Lebanon makes design requirement more stringent and will mostly affect civil engineers and developers. It's true that the added expense won't help with the unaffordable apartment prices nor the stagnating real estate market, however, people's lives depend on it.
Here are some explanations about the coefficient and the impact on cost.
The UBC seismic provisions contain six seismic zones, ranging from o (no chance of severe ground shaking) to 4 (10% chance of severe shaking in a 50-year interval). The shaking is quantified in terms of g-force (familiar to race car drivers and astronauts), the earth's gravitational acceleration. The diagram below is a way of describing seismic zonation.
The Lebanese Decree 7964 Article 3 changes the zone factor of Lebanon. As the latter increased from 0.2G (zone 2B) to 0.25G, the lateral forces increased with them. The earthquake lateral forces are proportional with the building weight and they are related by the seismic zone factor among other factor.
While the cost of the overall building won't change by more then 3%, the architectural constraints in building more then 10 floors will worsen. Bigger shear walls will decrease architectural space.
While some owners had already finish their permits, others only took permits for the basement floors. now stuck, with shear walls that are too small for the increased lateral loads, they are presented with two choices, either redesign or lighten the building. We present to you the least expensive way for the latter, while having many other advantages at the same time, the "Post-tension flat slab"
The Post tension solution
As the lateral forces are directly proportional to the weight of the and height of the building, using thinner slabs will affect greatly the results of the earthquake analysis.
The post-tension slab allows smaller building envelopes and lighter slab.
The overall savings of the system has just increased!
Send your drawings to [email protected] to price your hollowcore or post-tension slab project!