Type of Supports in Real Structures

After reading this blog, you will be able to identify and can execute different types of support in real structure in construction site.

                   During Engineering you have shown just the idealized form of supports but when you go to construction site you cannot identify and execute different type support in real structures. So in this article your confusion will be vanished. Here we have discussed the most important three (3) types of supports normally used and cause confusion.

Type of Supports in Different structures

(1) Fixed Support

                         Fixed support mean that it can resist and restrain all the possible movement (vertical, horizontal & bending moment) through the joint/support and the stresses generate in beam due to any type of loading can transfer from beam to column safely. Now we discuss fixed support in Reinforced Cement Concrete Structures (RCC) and Steel Structures:

Idealized form of Fixed support
(a) Fixed Support in RCC Structures

                                In RCC structure first column concrete is done upto beam bottom level and then after fixing the reinforcements of beam and slab with the column projected rebars then concrete it monolithically so that the member can act as a fixed unit. To identify that the support is fixed or hinged/pin in RCC beam-column joint or the column jointed with foundation, you must check the rebar detail in drawing and on site that if proper development length(Ld) is provided then and the desired ratio of concrete is followed at the site then the support will be consider is fixed. Because the reinforcement at the support will tell you about whether the support is fixed or hinged/pin. The proper development length (Ld) and required concrete grade will achieve sufficient bond/anchorage at that at that joint to resist all the stresses. This type of support is mainly designed to resist bending moment along with the other stresses. You can see the fixed support in the figure below:

Development Length of Steel bar - Formula of Development length- what is Development  length of steel - YouTube
Ld in Beam-Column Joint
Development length(Ld) provided in fixed support
www.sefindia.org :: View topic - Development Length of Isolated Footing  Rebars
Development length (Ld) at Column-Footing Joint
(b) Fixed Support in Steel Structures

                               The phenomena of fixed support that it will resist the possible movements will be same as in the RCC structures. The Steel Beam-Column connections or column-footing connections will be considered as fixed if the bolts or welds around the joint (around the flange and web) are fixed/applied throughout along with gusset plates at that joint/support. If the bolts or welds are fixed/applied only at the web section then it will consider as a hinged/pinned support because it will not resist all the movements (vertical, horizontal or bending moment) except the few one. This type of support is mainly designed to resist bending moment along with the other stresses. Through this type of bolting/welding you provided sufficient anchorage to resist all the stresses. The steel has to resist all the tension not concrete. You can see the Fixed Support in Steel Structure in figure/image below:

This image has an empty alt attribute; its file name is slide-9.jpg
Fixed Support in RCC (Provided Ld) and Steel (provided bolts and welds at flange and at web sections) Frame Structures
What is the difference between fixed support and pinned support? - Quora
Steel Frame Structure Fixed support at Column-Footing
(2) Hinge/Pin Support

                                 In this type of support only the horizontal and vertical movements are restrained but cannot resist bending moment. This type of support are not designed for taking any bending moments but just take the axial stresses (axial compression and axial tension). That’s why this type of support is mainly provided only in trusses. But if the bending is not the failure criteria of any member or if the bending moment is not generate sufficiently in any support that it can fail then we provide it in RCC and Steel Frames also:

Hinge/Pin Support in Truss Element
(a) Hinge/Pin Support in RCC-Bricks Structures

                                   You may have seen that in residential buildings or low storey buildings in which the load bearing component is brick walls then the beams and columns provided there by the unefficient contractor at some areas or in the whole structures is which may be not needed at all and also the structure is not properly designed by the structural engineer. If you look upon the reinforcement at beam-column joints or column-footing joints then you will find that they are not provided any development length or may be not sufficient to developed the required bond/anchorage at the joint. Because the tension is resisted by the steel not concrete. The concrete is also of very low Grade, so that support will not be considered as fixed but it will be a Hinge/Pin Support. But the loads are mainly taking by brick masonry walls that’s why the structure is stable. But you cannot allow this type of supports in RCC frame structures where the load bearing element is beam-column. You can see in given figure:

Fixed vs Hing/Pin Support in RCC/Brick Masonry Structures (the wrong one is hinge/pin becuase lack of Ld and the tensionisresistrd by steel not concrete)
(b) Hinge/Pin Support Steel Structures

                                  As we have discussed earlier that This type of support are not designed for taking any bending moments but just take the axial stresses (axial compression and axial tension). That’s why this type of support is mainly provided and designed for trusses. But it can be provide in Steel frames Beam-Column and Column-Footing joints when the bending is not the failure criteria. In this type of beam-column joints or column-footing joints the bolts/welds provided only at the web section or flange section of that element which is sufficient to resist the axial stresses. You can see in given figure below:

Hinge/Pin support in Steel Frame Structures (bolts provide only at web sections)
(2) Roller Support

                                  Roller support can resist only vertical forces. So it is provided only when there is only axially compressive forces are there. You have seen the simply supported beams/girders may be of Steel or RC. The idealized form of simply supported beam is one side is hinge and the other is roller (see image). We consider it because at the hinge/pin side of beam resist horizontal forces because lateral movement are not generate at the element just because of hinge/pin and the other side is roller because due to temperature changes and heavy loads there may be little lateral bit forces occur which causes expansion and bending. If we consider both side is hinged then the temperature  stresses in element will cause beam to crack and if we consider both side is roller than little component of lateral force can cause beam/girder to move horizontally which will be unstable. So when the beam which may be RCC or Steel which is lies just on both side support may be brick wall or RCC column but not casted monolithically then that will be an example of simply supported in which one side is roller and the other is hinge/pin support. You can see the roller support both in Steel and RCC structure given below:

Simply Supported Bridge Girders which acts one side is Hinge/pin and the other is Roller
Simply Supported Girders acts as as a Roller Support (Resist only vertical forces)
Idealized Simply Supported Beam/Girder

Watch the short video given below under these discussion Topics:

Types of Supports in Real Structures

Author: Engineer-Nisar

Civil Engineer

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