Civil Engineering Materials
Civil engineering materials are key components to the design and maintenance of civil structures. Most of these structures are large in scale such as bridges, buildings, and dams.
Materials that are widely used in the civil engineering practice include but are not limited to: reinforced concrete, asphalt, masonry, wood, structural steel, aluminum, and polymers.
Reinforced concrete is the most common civil engineering material. It is composed of concrete which is a combination of materials such as sand, fly ash, river rock, and cement.
Concrete which is a combination of materials such as sand, fly ash, river rock, and cement, is extremely strong when subjected to compression but behaves in a brittle manner when exposed to tension. The "reinforced" component is provided by steel rebar (Fig. 1). This rebar provides the tensile capacity to reinforced concrete structures.
The most desired quality of concrete is that it is readily available, and is usually composed of materials that can be found/produced locally. Concrete is also extremely durable under repeated loading conditions.
Concrete is an extremely heavy material. At 150 pcf, large scale concrete structures can experience more loading from self-weight than from live loads.
Structural steel is another civil engineering material that can be found in nearly all civil structures.
Steel is common in the design of beams, frames, columns, and trusses. Steel is strong in both tension and compression but is subject to many limit state checks in design. Steel girders can span much longer distances than reinforced concrete, but are more likely to buckle. A common application of structural steel is foundation design. Steel piles (HP shapes) can be driven into foundations (Fig. 2) to a minimum pile bearing capacity and then encased with reinforced concrete. This adds a great deal of flexural and axial capacity as well as protects the structural steel from corrosion.
Figure 2 is an example of steel pile foundation repair. Steel piling was driven closely together to prevent the road from sliding further. This is a common repair method for foundation slides.
The flexibility of steel in structural design makes it an economic material. Many steel structures can be built up from smaller steel components. Common examples of this are frame design and plate girder design. Frames can be composed of multiple steel shapes (W-Shapes, Angles, HSS, etc.) that are rigidly connected by welds and bolts. Plate girders are common in long span bridge design. Plate girders are composed of large plates (5 feet or more in height) that are spliced together with full penetration welds and high strength bolts.
Corrosion is the most common and most expensive problem with steel structures. Protective coatings must be maintained throughout the life of the structure or extreme section loss can occur. Steel is also susceptible to buckling. High shear loads can buckle the webs of steel I-beams if stiffeners are not designed. Steel beams are also subject to lateral torsional buckling (shown in Fig. 3) and flexural buckling if adequate bracing is not incorporated in design.
Figure 3 shows a set of plate girders after buckling laterally. The smaller buckled members were temporary bracing components that buckled in compression. Construction loads applied during lifting procedures and horizontal wind loads are common causes of lateral torsional buckling of plate girders. The strength of these flexural members is greatly reduced as a result of this buckling failure.