Portal Frame

INTRODUCTION

Frame is a structure elements composed of beams and column connected by rigid joints. The angle between the beam and column is usually 90.Figure 1 shows a simple frame which consists of a column and girder. Frames can be divided into two categories: braced and unbarred.

Girder Column

Figure 1 : Simple Frame

A braced frame is one in which the joint at each level are free to rotate but are prevented from moving laterally by attachment to a rigid element that can supply lateral restrain to the frame. An unbarred frame is one in which lateral resistance to displacement is supplied by the flexural stiffness of the beam and column.

PRINSIPLES

For single-bay frames many analyst define moment as positive when it produces compression stresses on the outside surface of the member, where inside is define as the region whitin the frame. The positive direction for shear is then arbitrarily defined, as shown by the arrows on figure 2. Axial force on a cross section is evaluated by summing all forces perpendicular to cross section. Forces acting outward from the cross section are tension forces: those directed toward the cross section are compression force.

V M

M

T T

M

M

V V

V C C

C V

C

V M

M

Figures 2 : Internal forces acting on section of the frame

For statically determinate frame, the internal forces (shear forces, axial forces and bending moments) can be calculated by using equation of equilibrium. =0

ΣFx ΣFy

=0

ΣMz

=0

OBJECTIVES

The main objectives for this experiment are 1. To investigate the behaviour of a portal frame experimentally under a given loading arrangement. 2. To compare the results obtained experimentally with theoretically results of the reactions bending moment, shear forces and axial forces.

EQUIPMENT AND APPARATUS

Figure 3 : Portal frame apparatus

1. Support Frame 2. Portal Frame 3. Dial Gauge 4. Varnier calliper 5. Ruler / tape measure 6. 1set of loads

PROCEDURE

The load cell is connected to the digital indicator.

The indicator is switched on. For the stability of the reading the indicator must be switched on 10 minutes before taking readings.

A load hanger is placed at the location where the load is to applied.

The indicator reading is noted. If it is not zero press the tare

A load is places on the load hanger

The indicator reading is recorded. This represents the horizontal reaction of the pinned support.

The load on the load hanger is increased and the horizontal reaction is recorded.

Step 7 is repeated for another 4 load increment.

The load on the hanger is decreased and the horizontal reaction is recorded.

Step 9 is repeated until all loads are removed.

RESULT

Width = 24 mm Thickness = 9mm Second moment area, I = 1.5 x 10

-12

Case 1[middle weight] Distance a = 30.5 mm Applied Load(N) 2 4 6 8 10

Horizontal trust (N) Experimental 0.14 0.28 0.43 0.54 0.68

Theoretical

Case 2[W at b] Distance b = 160 mm Applied Load(N) 2 4 6 8 10

Horizontal trust (N) Experimental 0.12 0.23 0.34 0.45 0.55

Theoretical

Case 3[W at c] Distance c = 385 mm Applied Load(N) 2 4 6 8 10

Horizontal trust (N) Experimental 1.22 2.48 3.75 5.01 6.29

Theoretical

Case 3[W at a, b, c] Applied Load(N) 2 4 6 8 10

Horizontal trust (N) Experimental 1.51 3.04 4.49 6.00 7.36

The graph show the relationship between the lo ad and trust

Theoretical

DISCUSSION

There are several factors that affecting the result of this experiment such as the air flow. As the equipment is very sensitive to external forces, a small flow of air will deflect the real value of the equipment such as the reading of the load. Although the deflection can be small, in smaller scale it will bring about to error that needed to be considered into calculation. To counter this problem the experiment should be done in closed room environment and not in open room. CONCLUSION

From the experiment we can conclude that when the load is place in the middle of the frame, the thrust downward will increase directly proportional to the load. The other case also shows similar thrust. As the bigger the load the bigger the horizontal thrust of the frame. To improve the experiment we should done the experiment in an closed room to prevent an error reading from the electronic reader as it is sensitive to alight air flow. The handle of load also is suspected to shake and really hard to statically. This experiment is an example of small scale industrial experiment to investigate the strength required to a bridge for example, in order to understand the mechanics of the load at certain part of a structure. The relationship between the load and thrust can be seen in the graph and the objectives of this experiment are accomplished.