The effects of the slab types to the behaviour of a reinforced concrete building with different structural systems

In recent years, increasing and housing needs due to the increasing of population and the requirements of business places are caused big problems in finding of the available residential areas. Because of the decreasing trend in the residential areas due to increased growth rate of cities, the construction of the multiple story buildings have become widespread. The modernization of construction techniques and technological developments in the construction sector provide an advantage of the construction of high-rise buildings. 92% of the total residential area of Turkey is located in the earthquake zone which is affected by an active fault line. Because of this, the earthquake resistance of buildings is the most important factor in our country. Cosidering the lateral and vertical loads acting on the structure, at design stage, the use of a different slab system can be the optimum solution to carry the structural loads safely, economically and satisfying architectural requirements for that building. The feasibility of the project on the site as well as choosing the true structural system are both important issues. In this respect, a realistic approach should be followed to select material properties for the chosen system. Within this study, we have chosen on different floors systems for a certain building which have modeled different types of slabs in the different structural system. "Turkish Specification for Buildings to be Built in Seismic Zones 2007" is followed to design the buildings as earthquake-resistant. The behavior of different types of slabs were investigated and also cost comparisons were made between them. Model sizes in the plan view of the chosen building are 16mx39.5m (=632m2). The height of the normal stories is 3m and the ground floor is 3.5m. "TS500 Requirements for Design and Construction of Reinforced Concrete Structures" were used to design the slabs and to determine the load combinations which are only vertical, windy, earthquake and lateral earth impulse loadings. All necessary combinations are taken into account while modeling. The structural loads were determined according to "TS 498 Design Loads for Buildings". The building is designed as an office building by which the live load participation factor is taken as 0.3, building and the importance factor as 1. The slab thickness of the plate slab system is 15cm and the beam cross-section sizes are 30cmx60cm. For the ribbed slab system model the width and height of the ribs are 10cm/30cm the slab thickness is 10 cm and the width of spacing is 40 cm, respectively. Beam sizes were used 60cmx40cm depending on loads. The thickness of the flat slab system is 25cm. Different live loads, such as 2 kN/m2 and 5 kN/m2, were affected over the buildings to evaluate the respondes. The concrete class of the entire system is selected as C30. This study consists of seven chapters; In the first chapter the scope and purpose of the study was given. In the second part, the different slab systems such as plate slab, ribbed slab and flat slab used for modeling were introduced also comparisons were made to examine the effectiveness of the structural system. Third part gives information about 'Specification for Buildings to be Built in Seismic Zones 2007'. The ductility levels of the structural systems and calculation methods used in seismic analysis were discussed. According to DBYBHY 2007, there are three methods Equivalent Seismic Load Method, Mode-Combination Method and Analysis Methods in the Time Domain to calculate earthquake loads Within this study equivalent seismic load method was used to calculate earthquake load affecting the structure. According to DBYBHY 2007, The Equivalent Seismic Load Method may be used for, • In the first and second seismic zones, buildings with torsional irregularity coefficient satisfying the condition ηbi ≤ 2.0 at every story and buildings with height less than 25 m. • In the first and second seismic zones, buildings with torsional irregularity coefficient satisfying the condition ηbi ≤ 2.0 at every story and at the same time without the type B2 irregularity, building height less than 40 m. • In the third and fourth seismic zones, all buildings, with building height less than 40 m. In DBYBHY 2007, structural systems are divided into three classes according to their ductility level: The systems with high ductility levels, normal ductility levels and mixed ductility levels. The cases of irregularity were introduced in the fourth section and examined the circumstances of the irregular building. In addition control of parameters which are effective in relative story drift and second order effect are described in this section. There are two main irregularities that were considered in the study; • The first one is irregularities in plan, consists following three types A1 - Torsional Irregularity, A2 - Floor Discontinuities, A3 - Projections in Plan. • The second one is Irregularities in elevation which consists of following three types are B1 – Interstory Strength Irregularity (Weak Story),B2 – Interstory Stiffness Irregularity (Soft Story), B3 - Discontinuity of Vertical Structural Elements. In fifth chapter established models were described. In the first section of this chapter; the general structure of the information was given in three different slab systems which are plate slab, ribbed slab and flat slab. After designing structural elements the effects of frame and wall frame systems have been investigated. The rigid frame systems have been designed as six floor and wall frame systems as twelve floor, respectively. Within this study, only model of flat slab was modeled with optimum dimensions with shear walls that is contains certain constraints in DBYBHY. Structures are modeled in three different slab types and analyzed with ETABS commercial software which is developed for structural analyses. According to the results of the analyses, reinforcements of the structural elements are selected and structural requirements are checked by using DBYBHY's. In the second section of this chapter, the effect of the three different slab system on the structural behaviour of the choosen building was analyzed. In the sixth chapter; the self weights of the models including live loads, periods and base shear forces were compared. In addition to that point, the cost of the steel and the concrete which was calculated in the first chapter for the choosen models were compared for one normal story. Additionally, in the second chapter of model section, we compared the effects of internal forces. Seventh chapter is the last part of this study; in which the results of the analyses were given and compared with each other.