English abstract
Shear walls are structural elements that are built parallel to the direction of the lateral loads. By their resistance to shear forces and overtuming moments, they transfer lateral loads, seismic and wind, to the foundation In this research, the behaviour of 14-story office building (35m long, 15m wide and 49.5m high) was studied using ETABS 16.2.1 commercial software under different load combinations. The RC frame consists of 200 mm thick flat slabs with 2x2 m drop panels each of 100 mm thick, 32 RC columns each with 550x550 mm, spaced by 5m centre-centre and 400x700 mm spandrel beams. Peripheral, 400mm thick, masonry walls (including 100mm cavity) were placed on top of the spandrel beams. No internal masonry walls were used. The first model was developed without shear walls, the model was tested twice; one time with the wind applied along the long direction of the building (y), this model was called 1a, and a model with the wind applied along the short direction of the building (x), this model was called 1b. It was found that when wind was applied along the long direction of the building (model 1a), it caused no failure even without shear walls. Contrarily, when the wind was applied in the short direction (model 1b) without the presence of shear walls, it caused failure to some columns and the building lateral displacement exceeded the code limits. Therefore, the wind in the x direction was considered as critical and used for testing and analysis of four different models. With exception of model 1 (no shear wall), each model consists of four different sub-models based on the length and thickness of the shear walls which ranged from 10-30m and 150-400mm respectively. The concrete characteristic compressive strength was 40N/mm2 steel characteristic tensile/compressive strength was 460N/mm-, the factor of safety of concrete was 1.5 and the factor of safety of steel was1.15. Three load combinations were adopted, as per Euro-code-2004, namely: (1) 1.35 DL+1.5 LL, (2) 1.35 DL+1.5 LL+0.9 WL and (3) 1.35 DL+1.05 LL+1.5 WL. The live load was 3.0 kN/m2 for general office use, the dead load of the floor and ceiling finishes was 2.5 kN/m and for the masonry walls was 4.275 kN/m2. For the wind load calculations, a basic wind speed of 31 m/sec was used.
A systematic test procedure was followed for testing all models and the design results of the 32 columns and the shear walls in each model were studied in terms of required reinforcement and building lateral displacements. For the tested models with shear walls, it was found that the shear wall length and thickness have almost no effect on the total quantities of columns' reinforcement when subjected to wind load; as all models showed almost equal amount of required columns' longitudinal reinforcement (about 38 ton) and concrete (480 m2) in all tested models with shear walls. In addition, all tested models with shear walls required only minimum stirrups for the three load combinations. Moreover, all tested models maintained lateral displacements within code limits. Therefore, the selection of the best model was based on the least lateral building displacement and the amount of required reinforcement and concrete of the shear walls. The largest building lateral displacement ranged from 55 mm (Model 2a: 150mm thick, 2.5x2x2m long) to 7 mm (model 4d: 400mm thick, 7.5x2x2m long) which fit within the ASCE code (ASCE/SEI 7-10, 2013). The shear walls' reinforcement ranged from 56 tons (model 2b: 200mm thick, 2.5x2x2m long) to 324 tons (model 4d: 400mm thick, 7.5x2x2m long). The volume of concrete ranged from 74m (model 2a: 150 mm thick, 2.5x2x2 m long) to 594m2 (model 4d: 400mm thick, 7.5x2x2m long). It was found that model 26 (200 mm thick, 2.5x2x2 m long) is the best followed by model 2c (300 mm thick, 2.5x2x2 m long) when the cost of concrete, cost of steel, and the rent of space in mo are high with maximum lateral displacements of 53 and 51 mm, and volume of concrete of 99 and 149 m, respectively. When the cost of concrete, cost of steel and the rent of space in mo are low, model 3b (200mm thick, 5x2x2m long) is the best, followed by 2d (400mm thick, 2.5x2x2m long). Models 36 and 2d exhibited least building lateral displacements, 30 and 53 mm, respectively with model 3b possessing smaller volume of concrete (108 < 110 m).
