BEC 303 STRUCTURE LABORATORY 5: PORTAL FRAME

1.0 OBJECTIVE1.) To establish the relationship between applied load and horizontal reaction at the pinned support. 2.) To observe the effect of the load position on the horizontal reaction.

2.0INTRODUCTIONPortal frame construction is a method of building and designing simple structures, primarily using steel or steel-reinforced precast concrete although they can also be constructed using laminated timber such as Glulam. The connections between the columns and the rafters are designed to be moment resistant, i.e. they can carry bending forces.Because of these very strong and rigid joints some of the bending moment in the rafters is transferred to the columns. This means that the size of the rafters can be reduced or the span can be increased for the same size rafters. This makes portal frames a very efficient construction to use for wide span buildings.Portal frame construction is therefore typically seen in warehouses, barns and other places where large, open spaces are required at low cost and a pitched roof is acceptable.Generally portal frames are used for single storey buildings but they can be used for low rise buildings with several floors where they can be economic if the floors do not span right across the building (in these circumstances a skeleton frame, with internal columns, would be a more economic choice). A typical configuration might be where there is office space built against one wall of a warehouse.Portal frames can be clad with all sorts of material but the most popular solution, for reasons of economy and speed, is some form of lightweight insulated metal cladding with cavity masonry work to the bottom 2m of the wall to provide security and impact resistance. The lightweight cladding would be carried on sheeting rails spanning between the columns of the portal frames.

3.0APPARATUS

Portal Frame Apparatus

5N Load

4.0PROCEDURE1. The load cell is connected to the digital indicator.2. The indicator is switched on. The indicator must be switched on for 10 minutes before taking readings for stability of the reading.3. A load hanger is placed at the location where the load is to be applied.4. The indicator reading is noted. The tare button is pressed if it is not zero.5. A load is placed on the load hanger.6. The indicator reading is recorded. This represents the horizontal reaction of the pinned support.7. The load is increased on the load hanger and the horizontal reaction is recorded.8. Step 7 is repeated for another four load increments.9. The result of the experiment is tabulated.

5.0EXPERIMENTAL RESULTS & CALCULATIONResults:

WaL1L3AB

Width of member, b = 25 mmThickness of member, h = 9 mmHeight of portal frame,L1 = 600 mmLength of portal frame,L3 = 600 mmDistance of load from support A, a = 500 mm

Load, W (N)Horizontal Reaction (N)

Experimental

50.2

100.4

150.6

200.8

251.0

Table 1

Calculations:The equations for the horizontal reaction at the pinned support A of a portal frame are given below:

Where;

Second moment of area,

Modulus of Elasticity, E = 200 x 10 3 N/mm2

Therefore;

(Note: 0.0417 is the slope of theoretical)Load, W (N)Horizontal Reaction (N)

ExperimentalTheoretical

50.20.209

100.40.417

150.60.626

200.80.834

251.01.043

Table 3By using the data from Table above, the graph of Load versus Horizontal Reaction at A supports are plotted which shown as below.The best straight line is drawn through the points plotted. From the graph plotted, the slope of the line, m is determined. (m represents the slope of experimental)

From the Graph, the slope of experimental is 0.04.Therefore, the percentage error of this experiment is:

6.0DISCUSSIONThe result obtained from the experiment 1 contains error by comparing it to theory. There is a variation between experimental and theoretical data, 4.08% error. The error occurred are due to several factors such as:- Inaccuracy reading from the digital indicator due to: Repeated adjustment of putting weight will occur the error of reading Wind load may affect the readings of indicator reading. Human error: The weights are not applied slowly. Wait for at least few seconds before take readings7.0CONCLUSIONFrom the result obtained, we conclude that the experiments consist of small variation errors which caused by few factors. By this, there are few suggestions in order to determine an accuracy of portal frame experiment. Such as: Care handling should be taken during application of the weights Readings are to be determined accuratelyFrom the experiment, it is obviously shown that the more loading apply to the portal frame, the bigger the displacement at the roller. And the more loading apply, the deflected shape and bending moments of the portal frame will be increasing.

8.0APPENDIX

Placing the load hanger.

Load had been added to the load hanger.

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