Q.
a) State three (3) functional requirements of external walls for framed buildings. (7 marks)
b) Illustrate using diagrams, the following type of walls for framed buildings:-
i) Curtain walling
ii) In-fill panels (18 marks)
(25 marks, 2011 Q3)
A.
(a)
Load bearing or framed building please see Load bearing wall vs framed wall building. Of course, load bearing wall needs to carry the load, rather the framed building structure the load is carried by the frame, not by the wall.
No matter which type of building, wall should fulfill its basic functions. There are among others:
A wall of a building should satisfy the following requirements, in design and construction, to perform its basic function and to have an enhanced life period.
1. STRENGTH
A wall should be strong enough to take up the loads safely due to its own weight, super imposed loads and lateral pressure such as wind.
2. STABILITY
It should be stable against overturning by lateral forces (due to wind load) and buckling caused by excessive slenderness.
3. WEATHER RESISTANCE
All the external walls, whether of load bearing or panel construction, should provide adequate resistance to rain, sun and wind penetration.
4. FIRE RESISTANCE
The walls should offer sufficient resistance to fire, as they behave as vertical barriers for spread of fire in the horizontal direction. So the walls should be made of such a material which neither ignite nor allow the spread of the fire through them.
5. HEAT INSULATION
It should be possible for walls to attain insulation against heat. For this, the walls are made either thicker, or cavity wall construction is employed. Heat insulating materials are also used in construction of walls.
6. SOUND INSULATION
The walls, both load bearing and non-load bearing, should be made of such materials and by such techniques, viz., cavity wall construction, so as to insulate building against indoor and outdoor noises.
7. PRIVACY & SECURITY
The walls, particularly external walls, should also provide sufficient privacy and afford security against burglary.
In the design and construction of walls, a balance between two primary considerations, namely strength and insulation against elements (such as heat, fire & weather), should be exercised.
Generally hollow concrete blocks or perforated bricks are used now days for construction of building walls, as it satisfies most of the requirements.
Ref:
7 Functional requirements a building wall should satisfy. CivilBlog.org, available at
i) Curtain walling
A curtain wall system is an outer covering of a building in which the outer walls are non-structural, but merely keep the weather out and the occupants in. As the curtain wall is non-structural it can be made of a lightweight material, reducing construction costs. When glass is used as the curtain wall, a great advantage is that natural light can penetrate deeper within the building. The curtain wall façade does not carry any dead load weight from the building other than its own dead load weight. The wall transfers horizontal wind loads that are incident upon it to the main building structure through connections at floors or columns of the building. A curtain wall is designed to resist air and water infiltration, sway induced by wind and seismic forces acting on the building, and its own dead load weight forces.
Curtain-wall systems are typically designed with extruded aluminum members, although the first curtain walls were made of steel. The aluminium frame is typically infilled with glass, which provides an architecturally pleasing building, as well as benefits such as daylighting. However, parameters related to solar gain control such as thermal comfort and visual comfort are more difficult to control when using highly glazed curtain walls. Other common infills include: stone veneer, metal panels, louvres, and operable windows or vents.
Curtain walls differ from store-front systems in that they are designed to span multiple floors, and take into consideration design requirements such as: thermal expansion and contraction; building sway and movement; water diversion; and thermal efficiency for cost-effective heating, cooling, and lighting in the building.
ii) In-fill panels
The infill wall is the supported wall that closes the perimeter of a building constructed with a three-dimensional framework structure (generally made of steel or reinforced concrete). Therefore, the structural frame ensures the bearing function, whereas the infill wall serves to separate inner and outer space, filling up the boxes of the outer frames. The infill wall has the unique static function to bear its own weight. The infill wall is an external vertical opaque type of closure. With respect to other categories of wall, the infill wall differs from the partition that serves to separate two interior spaces, yet also non-load bearing, and from the load bearing wall. The latter performs the same functions of the infill wall, hygro-thermically and acoustically, but performs static functions too.
The use of masonry infill walls, and to some extent veneer walls, especially in reinforced concrete frame structures, is common in many countries. In fact, the use of masonry infill walls offers an economical and durable solution. They are easy to build, attractive for architecture and has a very efficient cost-performance.
Today, masonry enclosures and partition walls are mainly made of clay units, but also aggregate concrete units (dense and lightweight aggregate) and autoclaved aerated concrete units are used. More recently, industry is also trying to introduce wood concrete blocks. Partition walls, made with both vertically and horizontally perforated clay blocks, represent two third of the corresponding market.
Infill walling is the generic name given to a panel that is built in between the floors of the primary structural frame of a building and provides support for the cladding system. Infill walls are considered to be non-load bearing, but they resist wind loads applied to the façade and also support their own weight and that of the cladding. Light steel walls using C sections are increasingly used as infill walling within both steel and concrete framed buildings, and have largely replaced masonry or timber alternatives.
An important feature of light steel infill walls is that the size and thickness of the light steel C sections can be varied depending on the height of the façade wall and the wind loadsacting on it. Large windows, parapets and other architectural features are made possible. Infill walls are generally installed on site as individual elements that are pre-cut to length but they can be pre-fabricated as large panels with the cladding already attached.
The same components may be used for internal separating walls, but here the main issues are fire resistance and acoustic insulation rather than resistance to loading. A nominal internal pressure is used in the design of internal separating walls.