Experiment NO 2: Portal Frames

Objective

The objective of this laboratory experiment is to study the behavior of a portal frame under

different end conditions.

Equipment and Apparatus

Portal Frame Apparatus (Pasco Advanced Structure Set- Force platform structure bracket,

members of size 4 and 5, screws, gusset plates)

Weights

Hanger

Load cells

Pulley system (wheel, string, connections, rods)

Load cells

PASCO 850 Universal Interface

Introduction

Portal frames are generally low-rise structures, comprising columns and horizontal or pitched

rafters, connected by moment-resisting connections. The connections between the columns and

the rafters are designed to be moment-resistant, i.e. they can carry bending forces. Portal frames

are frequently used over the entrance of a bridge and as a main stiffness element in building

design in order to transfer horizontal forces applied at the top of the frame to the foundation. On

bridges, these frames resist the forces caused by wind, earthquake, and unbalanced traffic

loading on the bridge deck. Portals can be pin supported, fixed supported, or supported by partial

fixity. The approximate analysis of each case will now be discussed for a simple three-member

portal. Resistance to lateral and vertical actions is provided by the rigidity of the connections and

the bending stiffness of the members, which is increased by a suitable haunch or deepening of

the rafter sections. This form of continuous frame structure is stable in its plane and provides a

clear span that is unobstructed by bracing. The shear force diagram shows how shear stresses

develop along the beam as a result of the applied load. If we know all the externally applied

loads and the corresponding reaction forces, obtaining the shear force diagram should be quite

straight-forward for a number of simple structural configurations. The shear force is one of the

ways by which the applied load is transmitted through the beam and is dissipated at the supports.

These are the internal shear stresses developing in order to keep adjacent cross-sections from

sliding past each other.

Figure 1: showing example of Reactions of Loaded Portal Frame

Figure 2: showing example of Shear Force Diagrams and Bending Moment Diagrams for each

member

Procedure

1- Select the end conditions of the portal frame.

2- Select the point where loading is to be applied (first horizontal than vertical

separately).

3- Now apply the load at the point selected for loading.

4- Get the readings from the capstone software

5- Unload the frame and shift the load cell to another leg and repeat the above (4), (5).

6- Again unload the frame and shift the load cell to the beam of the frame and repeated

(4), (5). (6).

7- Tabulate the observed reading and sketch the moment and shear diagrams as well as

the deflected shape for each member of the portal frame.

Lab Report Format:

Cover page

Purpose

Equipment and materials

Theory (expand on given Introduction)

Procedure

Data collected

Calculations

Discussion (comparison of experimental data to theoretical data)

Sources of error