# box beam

## Example 02: Maximum Concentrated Load a Box Beam Can Carry

**Problem**

A beam is built up by nailing together 25 mm thick planks to form a 200 mm × 250 mm box section as shown. The nails are spaced 125 mm apart and each can carry a shearing force of up to 1.3 kN. The beam is simply supported for a span of 3.6 m and to carry a concentrated load *P* at the third point of the span. The allowable shearing stress of the section is 0.827 MPa.

- Determine the largest value of
*P*that will not exceed the allowable shearing stress of the beam or the allowable shearing force of the nails. - What is the maximum flexural stress of the beam for the load
*P*computed in Part (1)?

## Example 01: Spacing of Screws in Box Beam made from Rectangular Wood

**Problem**

A concentrated load *P* is carried at midspan by a simply supported 4-m span beam. The beam is made of 40-mm by 150-mm timber screwed together, as shown. The maximum flexural stress developed is 8.3 MPa and each screw can resist 890 N of shear force.

- Determine the spacing of screws at
*A*. - Determine the spacing of screws at
*B*.

## Solution to Problem 595 | Spacing of Rivets or Bolts in Built-Up Beams

**Problem 595**

A concentrated load *P* is carried at midspan of a simply supported 12-ft span. The beam is made of 2-in. by 6-in. pieces screwed together, as shown in Fig. P-595. If the maximum flexural stress developed is 1400 psi, find the maximum shearing stress and the pitch of the screws if each screw can resist 200 lb.

## Solution to Problem 594 | Spacing of Rivets or Bolts in Built-Up Beams

**Problem 594**

A distributed load of *w _{o}* lb/ft is applied over a middle 6 ft of a simply supported span 12 ft long. The beam section is that in Prob. 593, but used here so that the 8-in dimension is vertical. Determine the maximum value of

*w*if

_{o}*f*≤ 1200 psi,

_{b}*f*≤ 120 psi, and the screws have a shear strength of 200 lb and a pitch of 2 in.

_{v}## Solution to Problem 593 | Spacing of Rivets or Bolts in Built-Up Beams

**Problem 593**

A box beam, built up as shown in Fig. P-593, is secured by screws spaced 5 in. apart. The beam supports a concentrated load *P* at the third point of a simply supported span 12 ft long. Determine the maximum value of *P* that will not exceed f_{v} = 120 psi in the beam or a shearing force of 300 lb in the screws. What is the maximum flexural stress in the beam?

## Solution to Problem 590 | Design for Flexure and Shear

**Problem 590**

A box beam carries a distributed load of 200 lb/ft and a concentrated load P as shown in Fig. P-590. Determine the maximum value of P if f_{b} ≤ 1200 psi and f_{v} ≤ 150 psi.

## Solution to Problem 586 | Design for Flexure and Shear

**Problem 586**

The distributed load shown in Fig. P-586 is supported by a box beam having the same cross-section as that in Prob. 585. Determine the maximum value of w_{o} that will not exceed a flexural stress of 10 MPa or a shearing stress of 1.0 MPa.

## Solution to Problem 585 | Design for Flexure and Shear

**Problem 585**

A simply supported beam of length L carries a uniformly distributed load of 6000 N/m and has the cross section shown in Fig. P-585. Find L to cause a maximum flexural stress of 16 MPa. What maximum shearing stress is then developed?

## Solution to Problem 571 | Horizontal Shearing Stress

**Problem 571**

For a beam with the same cross section as that in Prob. 570, plot the shearing stress distribution across the section at a section where the shearing force is V = 1800 lb.

## Solution to Problem 570 | Horizontal Shearing Stress

**Problem 570**

A uniformly distributed load of 200 lb/ft is carried on a simply supported beam span. If the cross-section is as shown in Fig. P-570, determine the maximum length of the beam if the shearing stress is limited to 80 psi. Assume the load acts over the entire length of the beam.