The Influence Line Diagram (ILD) for a force in a truss member is shown in the figure. If a Uniformly Distributed Load (UDL) of intensity of 30 kN/m longer than the span traverses, then the maximum compression in the member is

This question was previously asked in

KPSC AE 2017: Specific Paper

Option 2 : 23.186 kN

ST 22: Geotechnical Engineering

1632

20 Questions
20 Marks
15 Mins

**Approach: **To get the maximum compressive force place the UDL only up to the region of compressive force

**Concept:**

ILD (**Influence lines** are **important** in designing beams and trusses used in bridges, etc. Where loads will move along their span.

The **influence lines** show where a load will create the maximum effect for any of the functions studied.)

**Calculations: **

Given, ILD of the truss member

The intensity of UDL = 30 kN/m.

From the ILD figure, we know that the upper triangle is in the tension part and the **bottom triangle is in the compression part**.

The length of the compression span needs to be determined

From the similarity of triangles:

\(\frac{{0.29}}{x} = \frac{{0.58}}{{4 - x}}\)

\(x = \frac{4}{3}\)

In the above figure,

In order to get the maximum compressive force, UDL is placed till the compressive zone.

Force = UDL × (Area of the Compression triangle of ILD)

Maximum compressive force = 30 × (\(\frac{1}{2} \times 0.29 \times \left( {4 + \frac{4}{3}\;} \right)\) ) kN

= 30 × 0.7733

= 23.2 kN.

∴ Maximum compressive force = **23.2 kN.**