Concrete is one of the most versatile construction materials, offering potentially unlimited opportunities for developing diverse forms of construction. Concrete is what is known as a universal material, as its ingredients. namely cement, sand, aggregates, and water, are available all over the globe. Furthermore, concrete structures can be built with all different levels of technology, ranging from the simplest hand tools to computerized equipment. Concrete also has the excellent characteristics of fire resistance and durability and requires substantially less maintenance than other materials. Its mechanical properties can be enhanced by the use of steel reinforcement. Reinforced concrete construction makes use of the high compressive strength of concrete and the high tensile strength of steel reinforcement.
|Figure :1 Schematic elevations and plans for structural systems in reinforced concrete: a) moment-resisting frame; b) bearing-wall system; c) frame/shear-wall hybrid system.|
The structural (or framing) system is the skeleton of a building, and it supports the rest of the structure. Structural systems characteristic of reinforced concrete buildings are (see Figure 1)
- moment-resisting frames
- bearing-wall systems
- frame/shear-wall hybrid systems
|Figure :2 Moment Resisting Frame|
A moment-resisting frame (or moment frame) consists of columns and beams that act as a three dimensional (3-D) space frame system, as shown in Figure la. Both gravity and lateral forces are resisted by bending in beams and columns, while strong rigid joints between columns and beams have a special role in providing stability in moment frames. The frames are often infilled with masonry partitions (usually hollow concrete blocks or hollow clay tiles); such a system is called a concrete frame with masonry infills. The moment-frame system has been used often for office buildings in the world. The predominant use is in the five to ten storey range. Intermediate moment resisting frames (IMRF) and special moment resisting frames (SMRF) are other popular variants of moment resisting frames.
Bearing Wall System
|Figure :3 Bearing Wall System/ shear wall system|
A bearing-wall system consists of reinforced concrete bearing walls located along exterior wall lines and at interior locations as required (see Figure 1b). These bearing walls are also used to resist lateral forces, in which case they are called shear walls. Shear walls are designed to resist lateral forces from floor structures and transmit them to the ground. Ideally, these shear walls are continuous structures, extending from the foundation to the roof of the building. This system is usually characterized by a rectangular plan, with a centrally located elevator and stair core and uniformly distributed walls. Many residential and office buildings in Canadian cities utilize the bearing-wall system.
Frame/Shear Wall Hybrid System
|Figure :4 Frame/Shear Wall Hybrid System|
A frame/shear-wall hybrid system utilizes a complete 3-D space frame to support gravity loads and shear walls to resist lateral loads (see Figure 1c). The main lateral load resisting system consists of reinforced concrete shear walls forming the elevator core (central core formed by the elevators and stairs in the building), and additional walls located elsewhere in the building as required. The role of the concrete frame is to transfer gravity loads only, so it is often called the gravity frame. The columns typically support concrete flat slab structures or two-way slabs with beams. The interaction of the frame and shear walls is essential for limiting lateral deformations due to wind and earthquake loads. These buildings are generally characterized by a symmetrical plan of square, circular, or hexagonal shape with a centrally located elevator core. This system is commonly found in modern office and residential high-rise buildings throughout the world.