Design of highway bridges (third edition) part 2
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Design of highway bridges (third edition) part 2
PART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2fd4CHAPTER 13Reinforced Concrete Material Response and Properties13.1 INTRODUCTIONConcrete is a versatile building material. It can be shaped to conform to almost any alignment and profile. Bridge superstructures built OÍ reinforced and prestressed concrete can be unique one-of-a-kind structures for Design of highway bridges (third edition) part 2med and constructed at the job site, or they can be look-alike precast girders and box beams manufactured in a nearby plant. The raw materials of concDesign of highway bridges (third edition) part 2
rete—cement, tine aggregate, coarse aggregate, and water—arc found in most areas of the world. In many countries without a well-developed steel industPART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2 built of concrete are very competitive.Concrete bridges can be designed to satisfy almost any geometric alignment from straight to curved to doubly curved as long as tile clear spans arc not too large. Cast ill place (CIP) concrete box girders arc especially suited to curved alignment because of th Design of highway bridges (third edition) part 2eir superior torsional resistance and the ability to keep the cross section constant as it follows the curves. With the use of posttensioning, clear sDesign of highway bridges (third edition) part 2
pans of 150 It (45 m) arc common. When the alignment is relatively straight, precast prestressed girders can be utilized for multispan bridges, especiPART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2n-place girders monolithic with the deck slab (T-beams) can be used for clear spans up to about 65 ft (20 m). longer if continuity exists. Some designers do not like the underside appearance of the multiple ribs, but if the bridge is over a small waterway rather than a traveled roadway, there is les Design of highway bridges (third edition) part 2s objection.For smaller spans. CII* and precast culverts are a mainstay. Approximately one-sixth (100.0001 culverts with bridge spans greater than 20Design of highway bridges (third edition) part 2
ft (6 m) arc contained within the U.S.bridge inventory. Culverts perform extremely well, exhibit tew service problems, and are economical because the PART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2o, if formwork cannot be suitably supported, such as in a congested urban setting where traffic must be maintained, the design of special falsework to provide a construction platform may be a disadvantage.Longer span concrete bridges have been built using match-cast and cable supported segmental con Design of highway bridges (third edition) part 2struction. These structural systems require analysis and construction techniques that are relatively sophisticated and are beyond the scope of this boDesign of highway bridges (third edition) part 2
ok. In this chapter, short- to medium-span bridges constructed of reinforced and prestressed concrete are discussed.After a review of the behavior;of PART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2iled discussion of these two topics is given because of the introduction in the AASHTO (1994) LRFD Bridge Specification of a unified flexural theory for reinforced and prcstressed concrete beams and the modified compression field theory for shear resistance. In the development of the behavior models Design of highway bridges (third edition) part 2, the sign convention adopted for strains and stresses is that tensile values arc positive and compressive values are negative. This sign convention rDesign of highway bridges (third edition) part 2
esults in stress-strain curves for concrete that arc drawn primarily in the third quadrant instead of the familiar first quadrant.It is not necessary PART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2sions in the specification. In the chapters that follow, a number of example problems are given to illustrate the application of the resistance equations that arc derived. A concrete bridge deck with a barrier wall is designed followed by design examples of a solid slab, a T-beam. and a prestressed Design of highway bridges (third edition) part 2beam bridge.132 REINFORCED AND PRESTRESSED CONCRETE MATERIAL RESPONSETo predict the response of a structural clement subjected to applied forces, threDesign of highway bridges (third edition) part 2
e basic relationships must be established: (1 > equilibrium of forces. (2) compatibility of strains, and (3) constitutive laws representing the stressPART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2ied forces, there arc three equilibrium equations between the applied external forces and the three internal resisting forces: moment, shear, and axial load. When the external forces arc applied, the cross section deforms and internal longitudinal, transverse, and shear strains are (level Oped. Thes Design of highway bridges (third edition) part 2e internal strains must be compatible. Longitudinal strains throughout the depth of a section are related to one another through the familiar assumptiDesign of highway bridges (third edition) part 2
on that plane sections229230 13 REINFORCED CONCRETE MATERIAL RESPONSE AND PROPERTIESStirxXusOrganismExternal Force®. Loadsdeformation ot c-oes SectionPART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2ractice regarding material response; however, one should expect that changes may occur in the constitutive equations in the future as additional test data and/or new materials become available.13.3 CONSTITUENTS OF FRESH CONCRETEConcrete is a conglomerate artificial stone. It is a mixture of large an Design of highway bridges (third edition) part 2d small particles held together by a cement paste that hardens and will take rise shape of the formwork in which it is placed. Tile proportions of theDesign of highway bridges (third edition) part 2
coarse and tine aggregate. Portland cement, and water in the mixture influence the properties of the hardened concrete. The design of concrete mixes PART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2cular class of concrete from a scries of predesigned mixes, usually on the basis of the desired 28-day compressive strength. ff. A typical specification for different classes of concrete is shown in Table 13.1.before bending remain plane sections after bending. The longitudinal strains are related t Design of highway bridges (third edition) part 2o the transverse. shear, and principal strains through the relationships described in Mohr's circle of strain. The stress-strain relationships provideDesign of highway bridges (third edition) part 2
(he key link between the internal forces (which are integrations over an area of the stresses) and the deformations of the cross section. These interPART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2s a simple model used in psychology to illustrate that the manner in which individuals or groups respond to certain stimuli depends on their psychological makeup. In individuals, we often speak of one's constitution; in groups, the response depends on the constituents: in concrete, it depends on con Design of highway bridges (third edition) part 2stitutive laws. The analogy to concrete elements may be imperfect, but the point is that knowledge of the behavior of the material is essential to preDesign of highway bridges (third edition) part 2
dicting the concrete response of the element to external loads.Another point in regard IO the relationships in Figure 13.1 is that they involve both dPART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2f Design of highway bridges (third edition) part 2d mechanics that arc applied to specific cases. If the equations are properly written, then they lead to a set of unique correct answers. On the other hand, the constitutive equations are inductive as they are based on specific observations from which expressions are written to represent general beh Design of highway bridges (third edition) part 2avior. If the trends exhibited by the data are not correctly interpreted or an important parameter is overlooked, the predicted response cannot be verDesign of highway bridges (third edition) part 2
ified by experimental tests. As more experimental data become available, the constitutive equations change and the predicted response improves. The AAPART IIIConcrete BridgesS7d701b9fe5cf2e907fccllb261a2fd457d7Olb9foScf2o9O7fccllb261a2fd4S7(l701b9fe5cf2eỡ07fccllb2éla2fd457d701b9fe5cf2e907Rcllb261a2fGọi ngay
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