Xianyu Jin

Durability of Concrete Structures

Irreversible changes can occur to concrete structures due to combined environmental and service loads. This is caused by complex physical and chemical actions in addition to direct mechanical loads.

Basic principles of concrete structures

Based on the latest version of designing codes both for buildings and bridges (GB50010-2010 and JTG D62-2004), this book starts from steel and concrete materials, whose properties are very important to the mechanical behavior of concrete structural members. Step by step, analysis of reinforced and prestressed concrete members under basic loading types (tension, compression, flexure, shearing and torsion) and environmental actions are introduced. The characteristic of the book that distinguishes it from other textbooks on concrete structures is that more emphasis has been laid on the basic theories of reinforced concrete and the application of the basic theories in design of new structures and analysis of existing structures. Examples and problems in each chapter are carefully designed to cover every important knowledge point. As a basic course for undergraduates majoring in civil engineering, this course is different from either the previously learnt mechanics courses or the design courses to be learnt. Compared with mechanics courses, the basic theories of reinforced concrete structures cannot be solely derived by theoretical analysis. And compared with design courses, this course emphasizes the introduction of basic theories rather than simply being a translation of design specifications. The book will focus on both the theoretical derivations and the engineering practices.

Prestressed Concrete Structures

Prestressed concrete is made by introducing compressive stresses (prestress) into areas where an external load will produce tensile stresses. Before the established compressive stresses (prestress) offset, the concrete is not subjected to any tensile stresses.

Punching Shear and Bearing

Various slabs in reinforced concrete structures, such as flat floor slabs, spread footings, and pile caps (Fig. 1.4), may fail in the patterns shown in Fig. 9.1, under local compressions, which are perpendicular to the slabs and of high intensity. When the failure happens, circumferential cracks will appear on the top and bottom surfaces, and a truncated pyramid surrounded by the circumferential cracks will (or tends to) be separated from the surrounding part in the force direction. This type of failure is called punching shear failure, and the local load is called punching shear load; the dropped-out part is called punching shear failure pyramid.

Tension and Compression Behavior of Axially Loaded Members

Members subjected to axial tension at the geometric centers of their cross sections are called axially tensioned members. Typical examples in reinforced concrete structures include tensioned web elements and bottom chords in trusses, tie bars in arches, walls of internally pressured tubes, and sidewalls of tanks. Members subjected to axial compression at the geometric center of their cross sections are called axially compressed members. Typical examples are middle columns in multibay and multistory structures mainly sustained by permanent loads, compressed web members, and chords in trusses only loaded at the joints. Figure 4.1 illustrates common engineering applications of axially loaded members.

Serviceability of Concrete Structures

In the design of new concrete structures or in the appraisal of existing concrete structures, calculation for load-carrying capacity should be performed for all structural members in case any concrete members have reached their ultimate limit states due to strength failure or buckling. Concrete members can also reach their serviceability limit state, which would indicate a large deformation or undesirable vibrations or excessive crack width. Thus, to meet the functional requirements of the structures, it is necessary to control the deformation and the crack width and restrict their deviation within reasonable limits.

Compression and Tension Behavior of Eccentrically Loaded Members

In an eccentrically loaded member, the axial compressive load N c or axial tension load N t is applied at an eccentricity e0 on the member (Fig. 6.1a), which is equivalent to the combination of an axial load and bending moment M = N c e0 or M = N t e0 (Fig. 6.1b). The eccentrically loaded members include the eccentrically compressed members and the eccentrically tensioned members. nOpen image in new window n nFig. 6.1 nEccentrically loaded members. a An eccentrically compressed (or tensioned) member and b equivalent loading

Bending Behavior of Flexural Members

Flexural members are widely used in civil engineering shown here as reinforced concrete slabs, beams, stairs, and foundations in Fig. 1.4, retaining walls in Fig. 5.1, and girders, bent caps, and crash barriers in beam bridges in Figs. 5.2 and 5.3. Although flexural members have various section shapes, e.g., rectangular section, T-shaped section, box section, I-shaped section, and channel section, they can generally be categorized into two types according to their mechanical properties: rectangular and T-shaped sections (Figs. 5.4 and 5.5). Circular or ring sections are seldom used in practice.

Bond and Anchorage

As illustrated in Chap. 1, the prerequisite for combined action of concrete and steel bars requires a strong enough bond between the two materials to sustain the shear stress (called bond stress) caused by deformation difference (or relative slip) along the concrete–steel interface.