Composite building structures

1. INTRODUCTION

The structural system of a building is a complex three-dimensional assembly of interconnected discrete or continuous structural elements. The primary function of the structural system is to carry all the loads acting on the building effectively and safely to the foundation. The structural system is therefore expected to:

• carry dynamic and static vertical loads
• carry horizontal loads due to wind and earthquake effects
• resist stresses caused by temperature and shrinkage effects
• resist external or internal blast and impact loads
• resist and help damp vibrations and fatigue effects

In addition, any structural system is usually subject to the following constraints. It should:

• conform with the architectural requirements and those of the user or owner or both
• facilitate, as appropriate, the service systems, such as heating, ventilation and air conditioning, horizontal and vertical cabling, and other electrical and mechanical systems
• facilitate simple and fast erection of the building
• have adequate resistance to fire
• enable the building, foundation, and ground to interact properly
• be cost competitive all along the life cycle and not only at construction cost stage

Steel-concrete composite systems for buildings are composed of concrete components that interact with structural steel components within the same system. By their integral behaviour, these components give the required attributes of strength, stiffness, and stability to the overall system. Composite members, as individual elements of a system, have been in use for a considerable number of years. They consist of composite beams or trusses, encased or filled composite columns, and steel deck reinforced composite slabs. These members are generally used in steel structures, and their development as composite members is based on utilising the concrete that would normally be required for floor slabs with steel beams, or that would be required for fire-protective encasements with steel columns.

In most instances, the contribution of a composite member, which is developed to support only gravity loads, has been ignored in the overall system resistance for lateral wind or earthquake loads. The development of an overall system approach, where reinforced concrete and structural steel components can be used as effective contributing parts of the whole system, is more and more popular, especially for office or car park buildings or bridges among others. Considerable potential exists for evolving a variety of new structural systems in this way.

For typical structural systems used in building construction, whether they are steel, concrete, or composite, there are several subsystems, or components, common to all. These sub-systems can be grouped as follows:

1. floor systems
2. vertical load resisting systems
3. horizontal load resisting systems
4. structural connections

Section 3 discusses these systems in detail, concentrating on horizontal load resisting systems and structural connections. These topics are not covered by previous lectures.

The choice of a steel, concrete, or composite system for any particular project depends not only on system efficiency, material availability, cost, construction methods, and labour, but also on planning, environmental impacts and sustainability, and architectural and aesthetic criteria. It is thus impossible to reach definitive conclusions solely on the basis of a structural system evaluation. Section 2 describes several composite structural systems that have been used successfully on commercial building projects.