Construction Materials, Structures and Damage Types

Objectives

Upon completing this lesson, you will be able to:

1. Define construction materials and classify them by their composition types and uses.
2. List and describe three forces that can affect construction materials
3. List three properties of each material: concrete, steel and wood.
4. Describe two methods of construction.
5. List four types of structures.
6. List at least three characteristics of a building in each of the following four categories:
   • General
   • Architecture
   • Structural elements
   • Non-structural elements
7. List and describe two types of damage in a structure and their potential resulting failures.
8. Name and describe the four basic collapse patterns.

 

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   Construction Materials

Natural materials processed by man and used in the construction of buildings, which consist of structural and non-structural elements.

1.1 Classification by Composition

1. Stone: Marble, granite, slate.
2. Organic materials: Wood, plywood, paper, particleboard
3. Metal: iron, steel, aluminium.
4. Conglomerates: concrete, plaster, adobe, clay e. Ceramics: tiles
5. Glass: windows, glass block
6. Plastics: polyurethane, polyethylene, thermosetting adhesive

1.2 Classification by Use in the Structure

• Structural/load-bearing elements
• Decorative elements and facades or veneers
• Non-structural walls and partitions
• elements (roofing)

2. Forces Acting on Construction Materials

2.1 Tension

Forces that act to elongate or stretch a material.

Examples:

2.2 Compression

Forces that act to crush or compress a material.

Examples:

 

2.3 Shear

Forces acting in opposite, parallel directions and on different planes so that they cut or break a material.

Examples:

The forces of tension, compression and shear, and combinations of these, are those that affect materials and structures, with the potential to cause damage.

3. Properties of Construction Materials

3.1 Concrete

A construction material consisting of a mix of cement, rock, sand and/or other inert materials, water and a small amount of air.

Characteristics

• Resistant to Fire and Compression
• Weak under Tension and Shear
• Continues to harden with time
• Very heavy: one cubic meter (m3) weighs almost 3000KG

• Concrete cures by hydration, meaning that it needs water to harden. Once dry, concrete always develops cracks, which do not necessarily represent a failure. Concrete is strong in compression but weak in tension, which is why steel rebar is a necessary component of concrete beams, columns and floors.
• To appreciate the significance of concrete in construction and rescue operations, you must know how much it weighs: approximately 2,400-3,000 kg/mJ. On a smaller scale, a piece of concrete measuring 15 cm x 30 cm x 30 cm weighs approximately 34 kg.

3.2 Steel

Characteristics

• Can be bent without breaking (malleable)
• Resistant to Fire and Compression
• Easily conducts Heat. Sound and Electricity

3.3 Wood

Characteristics

• Easy to cut
• Light
• Not fire-resistant
• Good insulator (will not transmit electricity)
• Provides warning Creak before breaking

4. Methods of Construction

The type of construction will give some indication of the way a building will collapse. Experience has shown that there are patterns in the way structures collapse. Therefore, this knowledge is useful in determining the probable location of voids and spaces where victims may be trapped, and in selecting the methods to employ in extricating them. Buildings can be divided into two main categories: Framed and UnFramed.

4.1 Unframed Structures

Unframed structures are those in which the weight of the floors and roof are supported by the Bearing Walls.

Examples of this type of structures are brick and joist (support pillar for ceiling or floor) buildings and wood apartment buildings. As a general rule, these do not exceed seven stories in height. Rescue operations in unframed structure collapses are usually difficult, lengthy and dangerous. To the uninitiated, an extensive collapse gives the impression that the occupants have little chance of survival. Fortunately, rescues can be made because of the formation of voids created by structural members, strong objects such as machinery and heavy furniture, or a combination of these.

4.2 Framed Structures

Framed structures are erected by constructing a structural steel or reinforced concrete skeleton made of Horizontal beam and Vertical Column

The floors and/or roof are not dependent on the walls for support. Collapse can be more localized, but older concrete structures can suffer a pancake failure, and some steel structures with poor joints have overturned. The rescue teams face the same problem and seek out voids created by the collapse, as in unframed structures. Many buildings have elements of both unframed and framed structures. Most buildings have non-bearing walls. A common structure is one with exterior bearing walls with an interior framed system. A few examples would be tilt-up concrete walls with a wood roof and floors, and older brick or concrete wall warehouses with wood or concrete floors.

5. Structural Types

Based on experience with earthquakes and collapses, building types can be also divided into four separate groups, with each exhibiting a distinctive collapse pattern. These groups are:

5.1 Light Frame

• Residential homes and apartments of up to Four stories, and constructed mainly of Wood. The principal weakness is the Lateral strength of the walls and the connections.

• Rescuers operating in a light-frame building collapse should check for stability problems by looking for badly cracked or leaning walls and offset of the structure from the foundation, or a leaning first story in multi-floor dwellings.

5.2 Heavy Wall (URM) Unreinforced Masonry

These buildings are one to Six stories in height, and may be residential, commercial, industrial, or institutional. They have Heavy masonry walls and Wooder            floors. When

operating in an unreinforced masonry building make sure to check for loose and broken parapet walls and ornamental masonry, broken connections between walls and floors, cracked wall comers, and unsupported and partially collapsed floors.

5.3 Heavy Floor

Structures in this category can be residential, commercial, or industrial (concrete highway bridges). They have concrete frames and may be up to Twelve stories tall.

Rescuers should evaluate the stability of the structure by checking:

5.4 Pre-Cast Concrete

Buildings with fairly Heavy floors and some Heavy walls. Pre-cast structures may be commercial or residential and also include pre-cast parking facilities. These structures generally are one to Twelve stories in height. Principal weakness is in the interconnection of parts: slabs to walls/beams; beams to columns; walls to slabs, etc. Rescuers operating at a pre-cast building collapse should check for badly cracked walls, Beam to Column connections for broken welds and cracked corbels, column cracking at the top and the bottom of joints, and wall panel connections and shear wall connections at floor areas.

6. Characteristics of a Structure

After seismic activity or other force causes structural and non-structural damage, it is important to relate the characteristics of the structure to the damage it has suffered.

6.1 General

The general characteristics of a structure include the following elements:

• Occupy type
• Modifications to the original structure/plans (if applicable)
• Location of Utilities
• Contents
• Number of occupants

6.2 Architecture

Architectural characteristics of a structure include the following elements:

• Shape of building and foundation • Height and number of Floors • Number of Basement Levels • Major cantilevers
• Location of Chases (stairwells, elevator shafts and service chutes)
• Primary materials used

6.3 Structural Elements

The structural or load-bearing elements of a structure include the following:

• Columns • Beams, girders, trusses, joists, rafters, purlins, studs • Floor slabs, roof

• Load-bearing walls
• Foundations

6.4 Non-structural Elements

• Non-load-bearing walls, partitions, in-fill
• Windows, doors and other openings (fenestrations)
• Fa9ades, veneers, parapets, and other

7. Damage Types and Potential Hazards

Damage to buildings can be categorized as structural and non-structural. Damage affects the Structural elements of a building, and likewise, non-structural damage affects the nonstructural elements of a building. However, both types of damage are capable of causing injury, death, contamination and other hazards.

7.1 Structural Damage

• Total structural collapse
• Leaning floors, roofs and walls
• Collapsed Floors and Roofs
• Collapsed columns in one or more floors
• Substantial, permanent Lateral shift in the structure
• Cracks in column floor slabs
• Cracked foundation
• Cracked elevator shaft

7.2 Non-Structural Damage

• Generalized cracking
• Cracked or fallen Exterior facades and Veneers
• Fallen staircases
• Shift in the elevator shaft
• Damaged Utilities
• Building signs and balconies

7.3 Types of Hazards

In damaged, partially and fully collapsed structures, we can identify three types of hazards:

• Falling: Part of the structure or its contents are in danger of falling.
• Collapse: The volume of enclosed space made by the structure will be reduced, as stability is lost.
• Other: Electricity, water, fuels, toxic gases (carbon monoxide), hazardous materials (asbestos), biohazards (industrial, medical), etc.

8. Basic Collapse Patterns

8.1 Cantilever

Results from a wall collapse which allow a floor or roof assembly to Drop Partially, but to remain Suspended above the

floor or base below on the side where the wall failed. The opposite end of the floor assembly remains attached to the wall and at its original connection point. This type of collapse is extremely unstable and dangerous.

8.2 Lean-to

Found where a wall failure causes a floor or roof section to fall completely on one side. while the other end remains Supported. This collapse                usually results in a

Triangular void. Remember that the remaining supported end of the fallen section may be precariously supported.

8.3 Pancake

Refer to multi-floor collapses where several floor slabs completely fail and Stack up on top of each other. The resulting voids are Limited in space and are difficult to access, especially in concrete structures.

8.4 V-Shape

This collapse will be created when a floor assembly collapses in the Middle due to failure of centre supports or overload of the floor.

The result is two identifiable voids which are created on Each side of the broken floor assembly.

Identify the Failure Types

Identify the failure types above and whether they are structural or non-structural and reply in comments about what you learned.