Ch 12 pg 333-338 lightweight construction

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Questions and Answers

Which of the following statements accurately describes the primary difference between standard and lightweight construction?

Standard construction uses lighter materials compared to lightweight construction.

Lightweight construction primarily uses heavier beams and joists than standard construction.

Standard construction is more cost-effective than lightweight construction.

The main difference lies in the mass of the materials (correct)

What materials are typically used in Class 3 construction?

Brick and joist construction. (correct)

Wood frames with plywood sheathing.

Steel frames with aluminum sheathing.

Concrete blocks with steel reinforcement.

What is a significant drawback of standard construction concerning wood beams?

They have a maximum span of approximately 50ft.

They are more prone to sudden structural failures.

They provide greater energy efficiency.

The maximum span of a wood beam is about 25ft. (correct)

Which feature of standard roof construction helps prevent sudden collapse during a fire?

The sheathing burns away before the beams fail. Signup and view all the answers

Why is standard construction often considered expensive?

The amount of material needed is substantial. Signup and view all the answers

What characteristic of a truss contributes to its vulnerability in firefighting scenarios?

Thinner members leading to reduced mass Signup and view all the answers

How does the design of a truss affect its behavior under fire conditions?

It allows for faster heating of its smaller components. Signup and view all the answers

Why might architects prefer using trusses in construction despite the risks presented in firefighting?

Trusses can be constructed quickly and cost-effectively. Signup and view all the answers

What is a primary disadvantage of using a truss as compared to a traditional beam when subjected to extreme conditions?

Trusses have less mass, resulting in quicker failure under fire. Signup and view all the answers

What role do connectors play in a truss system?

They help join short sections of material to span large areas. Signup and view all the answers

Which type of connector is NOT mentioned as being used in truss construction?

Welded joints Signup and view all the answers

How can connectors negatively impact the material they are attached to?

By conducting heat to the inside of the material. Signup and view all the answers

What is a potential consequence of connector failure in a truss?

Failure of the truss itself. Signup and view all the answers

Which characteristics make connectors advantageous for truss construction?

They are short sections of material, which are less expensive. Signup and view all the answers

What should firefighters do upon discovering trusses in a building?

Immediately report to the Incident Commander Signup and view all the answers

Which of the following factors does NOT influence the decision to commit firefighters to roof operations?

Type of building materials used Signup and view all the answers

Why are lightweight roofs particularly dangerous to firefighters?

They can collapse suddenly without obvious signs of failure Signup and view all the answers

What is indicated by the presence of a truss during firefighting operations?

A signal for caution and increased risk Signup and view all the answers

What should be assessed before committing interior forces to firefighting operations when trusses are present?

The presence of any civilian life hazards Signup and view all the answers

What happens to a truss when any of its members or connections fail?

The truss may collapse suddenly. Signup and view all the answers

Why are triangles significant in the design of trusses?

Only one triangle can be formed from three pieces of the same length. Signup and view all the answers

What role does the top chord serve in a truss?

It supports compressive loads. Signup and view all the answers

In the analogy of a hunter's bow as a truss, what represents the bottom chord?

The bowstring under tension. Signup and view all the answers

What is the main consequence of isolating a single weakness in a truss structure?

It may cause a total failure of the truss. Signup and view all the answers

What is a significant risk when hip rafters rest on an end wall of a bowstring truss?

Injury or death of firefighters even when outside the collapse zone Signup and view all the answers

What should be the minimum collapse zone at end walls with hip rafters?

2 1/2 times the height of the wall Signup and view all the answers

What is one recommended action if maintaining the collapse zone is not feasible?

Firefighters should operate from flanking positions, away from the wall. Signup and view all the answers

What potential danger must firefighters be aware of when operating above an end wall?

Eruption of a fireball during roof collapse Signup and view all the answers

Which area is considered safer for firefighters during a truss wall collapse?

Off to the sides in flanking positions Signup and view all the answers

What is the most dangerous style of roof construction in modern styles according to incident rates?

Bowstring trusses Signup and view all the answers

What is a common occupancy type where a bowstring truss roof is expected to be found?

Bowling alleys Signup and view all the answers

What significant structural characteristic can result from the failure of a single bowstring truss?

Opening of a 40-ft hole Signup and view all the answers

Why must personnel be removed from both the roof and interior operations surrounding the bowstring truss roof during heavy fire?

To ensure their safety due to potential structural failure Signup and view all the answers

What appearance do bowstring trusses typically present, despite being constructed from smaller materials?

Massive, solid timber Signup and view all the answers

Up until the ____ class 3 and 5 buildings used 2x10s and heavy steel I beams

1960s Signup and view all the answers

The top chord of a truss bears a _____ load and the bottom under tension, acts to pull the top chord into position. The web transmits the load aback to the other two at short intervals

Compressive Signup and view all the answers

Study Notes

Construction Techniques Overview

Building construction is categorized into Standard and Lightweight methods.
Standard Construction utilizes heavier materials such as robust beams and joists, while Lightweight Construction employs lighter components.
The choice of construction method significantly impacts material weight and structural characteristics.

Common Construction Types

Class 3 Construction: Involves brick and joist construction.
Class 5 Construction: Consists of wood frame structures.
These construction types typically feature large members like 2x10 joists or steel I-beams.
Most prevalent construction methods in the U.S. up until the 1960s.

Standard Roof Construction Elements

Sheathing consists of 1x6in or 5/8in plywood.
Joists measure 2x10 and are spaced 16in apart.
Characterized as a solid roof type, with reduced risk of sudden collapse due to resilience against fire.

Drawbacks of Standard Construction

Span Limitations: Maximum span for wood beams is about 25ft.
Cost: Standard roofs incur high expenses due to larger material requirements.

Challenges with Truss Systems

Truss design favors lightweight materials but poses risks in fire situations, leading to potential rapid failures.
Lack of Mass: Compared to standard beams, trusses are more susceptible to failure under fire due to their lighter design.

Connector Vulnerabilities

Trusses with connectors (e.g., gusset plates, metal pins, or through bolts) can fail if compromised, facilitating rapid heat transfer and weakening the structure.
Failure of one component can jeopardize the integrity of the entire truss system.

Truss Structure and Safety Risks

Trusses are composed of interconnected elements (top chord, bottom chord, web members) arranged in triangles for stability.
If any component fails, it can lead to catastrophic collapse. The entire system is only as strong as its weakest part.
Trusses must maintain intact connections for stable structural support during fire events.

Firefighters’ Considerations

Awareness of truss presence is critical for firefighter safety; early collapses are a significant risk.
Size-up decisions should incorporate fire severity, duration, and whether the truss has been compromised.

Types of Trusses: Bowstring Trusses

Bowstring truss roofs are notably hazardous and are often found in large public structures like bowling alleys, auto dealerships, and supermarkets.
Characterized by a hump shape that may not be visible from the street, they can collapse suddenly, creating expansive openings.

Bowstring Truss Safety Issues

Hip rafters resting on end walls can produce explosive collapses, thus creating zones of danger that extend beyond perceived boundaries.
A collapse zone must be at least 2.5 times the height of the wall to ensure safety.
Firefighters should operate from flank positions or elevated platforms when possible to mitigate risks during emergencies.

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Description

Explore the differences between Standard and Lightweight construction techniques in this quiz. Learn about construction materials, types, and their implications on building design. Test your knowledge on Class 3 construction and the materials used in various building types.