Question

Slabs, columns, beams, roofs and foundations are structural elements in architecture. And they have different types and dimension.

According to structure their shape, types and dimensions can be changed. According to these characters… what’s the importance of these elements.

Note that: (hint)

• Load carrying
• Distances
• Materials
• Try to make a research about these elements and civil engineering calculations. !

• Make a research about question above.
• You are free to use photos diagrams figures on your report be sure that explanation is included to your attachment.

Answer 1

To design any structure even from the perspective of an architecture, structural design is must and it should be given atmost importance. Structural design is the methodical investigation of the stability, strength and rigidity of structures. The basic objective in structural analysis and design is to produce a structure capable of resisting all applied loads without failure during its intended life. Following are the points explaining importance of these structural elements.

1. Slabs:

Slab is an important structural element which is constructed to create flat and useful surfaces such as floors, roofs, and ceilings. It is generaaly a horizontal structural componenet.

Commonly, slabs are supported by beams, columns (concrete or steel), walls, or the ground. The depth of a concrete slab floor is very small compared to its span.

Types of loads acting on a slab include:

1. Dead load of the slab
2. Live load
3. Floor finish load
4. Snow load in the case of roof slab
5. Earthquake loads

Load Transfer Mechanism in Slabs

The forces transfer from slab to beams occur either in one way or in two ways.Slabs may be supported by columns only, in this case two way action will prevail. If the ratio (Longer side / shorter side) < 2 it is considered as 2-way slab, and if (Longer side / shorter side) > 2 then it is considered as 1-way slab. Following diagram shows load transfer mechanism.

2. Beams

beam is a horizontal structural element that withstand vertical loads, shear forces and bending moments. The loads applied to the beam result in reaction forces at the support points of the beam. The total effect of all the forces acting on the beam is to produce shear forces and bending moment within the beam, that in turn induce internal stresses, strains and deflections of the beam.

Types of Loads on Beams

1. Self-weight of the beam
2. Dead load includes point load for instance column constructed on beam, distributed load for example setting slabs on a beam.
3. Live load
4. Torsional load

Load Transfer Mechanism in Beams

They transfer loads imposed along their length to their end points where the loads are transferred to columns or any other supporting structural elements. Following diagram shows the load transfer mechanism in a beam.

3. Columns

Column is a vertical structural member that carry loads mainly in compression. It is assumed to be the most crucial structural member of a building because the safety of a building rest on the column strength. This is because failure of column would cause progressive collapse in buildings whereas such event would not occur when other members fail.

Columns transfer vertical loads from a ceiling, floor or roof slab or from a beam, to a floor or foundation. They also carry bending moments about one or both of the cross-section axes.

Types of Loads on Columns

1. Self-weight of the column multiplies by number of floors
2. Self-weight of beams per running meter
3. Load of walls per running meter
4. Total Load of slab (Dead load + Live load + Self weight)

Loads Transfer Mechanism in column

Since the columns are supported by foundation; the load relocated from the all components to the columns, will be transferred from the column through the column necks adjacent to the footing in the form of axial force. Moreover, Columns transfer lateral loads to foundations as well, when such loads are imposed. Lastly, It will transfer moment and shear also to the footing. Following diagram shows the load transfer mechanism via all the different strucral elements. (Slab --> Beam --> Column --> Foundation --> Soil)

4. Footings / Foundation

Footings are structural elements that transmit load of entire superstructure to the underlying soil below the structure. Footings are designed to transmit these loads to the soil without exceeding its safe bearing capacity. Thus, prevent excessive settlement of the structure to a tolerable limit, to minimize differential settlement, and to prevent sliding and overturning.

Types of Loads on Footings

1. Dead load
   • Self-Weight of the elements
   • Superimposed loads such as finishes, partitions, block work, services.
2. Live load
3. Impact load
4. Snow load
5. Wind load
6. Earthquake force
7. Soil pressure
8. Rain loads
9. Fluid loads

Load Transfer Mechanism in Footing

Soil is the root support of the footing. All the forces that come in contact with the footings will be transferred to the soil. The soil shall bear these loads by the aspect known as bearing capacity (bearing capacity is the ability of soil to withstand against the applied loads, and support the structure without undergoing shear failure) . The bearing capacity changes from one type of soil to another and it is the key factor in estimating the size of footings. Following diagram shows how load is transfered to footings and then to the soil.

Following are the three methods of structural design:

• Working stress method (WSM)
• Ultimate load method (ULM)
• Limit state method (LSM)

1. Working stress method (WSM)

This was the traditional method of design not only for reinforced concrete, but also for structural steel and timber design. The method basically assumes that the structural material behaves as a linear elastic manner, and that adequate safety can be ensured by suitably restricting the stresses in the material induced by the expected “working loads” on the structure. The design usually results in relatively large sections of structural members, thereby resulting in better serviceability performance under the usual working loads.

2. Ultimate load method (ULM)

With the growing realization of the shortcomings of WSM in reinforced concrete design, and with increased understanding of the behavior of reinforced concrete at ultimate loads, the ultimate load of design is evolved and became an alternative to WSM. In this method, the stress condition at the site of impending collapse of the structure is analyzed, and the nonlinear stress-strain curves of concrete and steel are made use of.

This method generally results in more slender sections, and often economical designs of beams and columns, particularly when high strength reinforcing steel and concrete are used. However, the satisfactory ‘strength’ performance at ultimate loads does not guarantee satisfactory ‘serviceability’ performance at the normal service loads. The designs sometimes result in excessive deflections and crack-widths under service loads, owing to the slender sections resulting from the use of high strength reinforcing steel and concrete.

3. Limit state method (LSM)

Unlike WSM which based calculations on service load conditions alone, and unlike ULM, which based calculations on ultimate load conditions alone, LSM aims for a comprehensive and rational solution to the design problem, by considering safety at ultimate loads and serviceability at working loads. The LSM philosophy uses a multiple safety factor format which attempts to provide adequate safety at ultimate loads as well as adequate serviceability at service loads, by considering all possible ‘Limit State’.

Limits States

A limit state is a state of impending failure, beyond which a structure ceases to perform its intended function satisfactorily, in terms of either safety of serviceability i.e. it either collapses or becomes unserviceable.There are two types of limit states:

Limit states of collapse:- which deal with strength, overturning, sliding, buckling, fatigue fracture etc.

Limit states of Serviceability: – which deals with discomfort to occupancy and/ or malfunction, caused by excessive deflection, crack width, vibration leakage etc., and also loss of durability etc.