Developed to comply with the fifth edition of the AASHTO LFRD Bridge Design Specifications ––Simplified LRFD Bridge Design is "How To" use the Specifications book. Most engineering books utilize traditional deductive practices, beginning with in-depth theories and progressing to the application of theories. The inductive method in the book uses alternative approaches, literally teaching backwards. The book introduces topics by presenting specific design examples. Theories can be understood by students because they appear in the text only after specific design examples are presented, establishing the need to know theories. The emphasis of the book is on step-by-step design procedures of highway bridges by the LRFD method, and "How to Use" the AASHTO Specifications to solve design problems. Some of the design examples and practice problems covered include: Load combinations and load factors Strength limit states for superstructure design Design Live Load HL- 93 Un-factored and Factored Design Loads Fatigue Limit State and fatigue life; Service Limit State Number of design lanes Multiple presence factor of live load Dynamic load allowance Distribution of Live Loads per Lane Wind Loads, Earthquake Loads Plastic moment capacity of composite steel-concrete beam LRFR Load Rating Simplified LRFD Bridge Design is a study guide for engineers preparing for the PE examination as well as a classroom text for civil engineering students and a reference for practicing engineers. Eight design examples and three practice problems describe and introduce the use of articles, tables, and figures from the AASHTO LFRD Bridge Design Specifications. Whenever articles, tables, and figures in examples appear throughout the text, AASHTO LRFD specification numbers are also cited, so that users can cross-reference the material.
The 2011 PCI Bridge Design Manual provides preliminary design charts for selecting the girder size and number of prestressing strands for a given span length and beam spacing but only for [small leter f with hook]ʹ[subscript c] = 8,000 psi (55.2 MPa). This single strength limits the use of the charts, particularly for states considering ultra-high performance concrete (UHPC). Accordingly this dissertation presents a simplified procedure to develop preliminary design charts for prestressed concrete bulb-tee girders considering service load stress limits, flexural strength and stresses at release. The results for a BT-72 beam are first compared with the 2003 PCI design charts originally developed based on the AASHTO Standard Specifications. The procedure is then adapted to the AASHTO LRFD Bridge Design Specifications and verified with the prevailing 2011 PCI design charts. Finally, new LRFD charts are generated for NSC, HPC, and UHPC with 0.5, 0.6, and 0.7-in. (13, 15 and 18 mm) strands for simple and two-span continuous bridges to illustrate the simplified procedure and potential impact of UHPC, larger strand size, and continuity on bridge girders. The new LRFD charts are shown to be accurate for the design assumptions made since an excellent agreement (within 2% and 4%) resulted between the preliminary design charts developed in this study and those given in the 2003 and 2011-PCI Bridge Design Manuals. The "transition point" is identified which provides the information needed for a designer to distinguish the zones between fully prestressed (uncracked), partially prestressed, and non-prestressed (cracked) members. The preliminary design charts demonstrate the effect of using UHPC and/or larger strand size and/or two-span continuous layouts. The effect of implementing continuity with the combination of UHPC and a larger strand diameter was shown to be much more significant than just increasing the concrete compressive strength or the strand diameter or using two-span continuous layouts. However, the use of longer full-span girders poses significant challenges for fabrication, transportation, erection, span-to-depth ratios, and live and dead load deflections of prestressed concrete bridges and, consequently, should be considered carefully for the final design of the bridge.
The up-to-date guide to applying theory and specifications to real-world highway bridge design Design of Highway Bridges, Second Edition offers detailed coverage of engineering basics for the design of short- and medium-span bridges. Based on the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications, it is an excellent engineering resource. This updated edition features: * Expanded coverage of structural analysis, including axle and lane loads, along with new numerical analytic methods and approaches * Dozens of worked problems, primarily in Customary U.S. units, that allow techniques to be applied to real-world problems and design specifications * Revised AASHTO steel bridge design guidelines that reflect the simplified approach for plate girder bridges * The latest information on concrete bridges, including new minimum reinforcement requirements, and unbonded tendon stress at ultimate and losses for prestressed concrete girders * Information on key bridge types, selection principles, and aesthetic issues * Problems and selected references for further study * And more From gaining quick familiarity with the AASHTO LRFD specifications to seeking broader guidance on highway bridge design--this is the one-stop, ready reference that puts information at your fingertips.
Glass fiber reinforced polymer (GFRP) materials have emerged as an alternative material for producing reinforcing bars for concrete structures. GFRP reinforcing bars offer advantages over steel reinforcement due to their noncorrosive nature and nonconductive behavior. Due to other differences in the physical and mechanical behavior of GFRP materials as opposed to steel, unique guidance on the engineering and construction of concrete bridge decks reinforced with GFRP bars is needed. These guide specifications offer a description of the unique material properties of GFRP composite materials as well as provisions for the design and construction of concrete bridge decks and railings reinforced with GFRP reinforcing bars.
Covers seismic design for typical bridge types and applies to non-critical and non-essential bridges. Approved as an alternate to the seismic provisions in the AASHTO LRFD Bridge Design Specifications. Differs from the current procedures in the LRFD Specifications in the use of displacement-based design procedures, instead of the traditional force-based "R-Factor" method. Includes detailed guidance and commentary on earthquake resisting elements and systems, global design strategies, demand modeling, capacity calculation, and liquefaction effects. Capacity design procedures underpin the Guide Specifications' methodology; includes prescriptive detailing for plastic hinging regions and design requirements for capacity protection of those elements that should not experience damage.
According to the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications, a bridge is defined to be fracture critical when a failure of a tension component will result in the collapse of the bridge. In the case of a twin box girder bridge, the tension flanges in the positive moment portion of the bridge, as well as the webs, are considered to be fracture critical elements. Due to this classification, those bridges are subjected to stringent inspections at least every two years. Those inspections are crucial for ensuring the safety of the bridge, yet are expensive and time consuming. Multiple cases of FCBs (Fracture Critical Bridge) that have experienced a fracture in one of their elements without collapse have encouraged owners of those bridges to question the validity of AASHTO's requirements. The Texas Department of Transportation is interested in indentifying when a fracture of an element could lead to a catastrophic collapse of a bridge. A better understanding of fracture critical bridge behavior may allow TxDOT and other state DOTs to reduce the frequency of the inspections, which could potentially reduce the cost of an otherwise attractive bridge design. The goal of this research project is to determine the level of redundancy of twin box girder bridges. Simplified analytical methods and guidelines that will conservatively estimate the behavior of such bridges will be presented in this thesis. Those guidelines will be one of the tools that an engineer in practice could use to determine if a bridge is prone to collapse following the failure of a fracture critical component. A full-size bridge has been constructed at the Ferguson Structural Engineering Laboratory to test the response of these systems following a simulated fracture. A series of tests were conducted to determine the response of the bridge in the event of a tension flange fracture. The results provided important information for the development of the simplified methods. The FSEL test bridge performed extremely well throughout all the testing and supported a load of over four times the AASHTO design truck load. Several elements contributed to create alternative load paths that could sustain the entire applied load with a full-depth fracture of one of its two girders. The large section of the concrete railing above the fractured girder acted as an inverted beam and transmitted a portion of the load back to the supports once the expansion joint closed due to the downward deflection of the bridge. The concrete deck acted as a shear diaphragm and also transferred significant loads in both horizontal directions. Because the performance of the test bridge far exceeded the AASHTO criteria, and because this behavior can be computed using the simplified methods presented in this thesis as well as through detailed finite element models, consideration should be given to revising the current AASHTO specifications and to developing alternate inspection and maintenance requirements that accurately reflect the redundancy available in various types of fracture critical bridges.