Computer Aided Bridge Engineering

The present book ‘Compute Aided Bridge Engineering’ is for the design of Pre-stressed Concrete (PSC) I-Girder (I-Beam) and PSC Box-Girder Bridges. In this volume, the real project design calculations for deck-girder superstructure are presented along with the design of Abutment and Pier with Pile Foundation as the bridge substructure.

The book is proposed to be read in association with processing the design work by using the computer software ASTRA Pro as referred to in the book. The book describes two essential facets of the work, which are ‘Analysis of the Grillage Model of the Deck-Girder Superstructure’ and the subsequent ‘Design of Deck Slab and PSC I-Girder’. Whereas the software provides three facets of the work, first is the ‘Analysis of the Grillage Model of the Deck-Girder Superstructure’, second is the ‘Design of Deck Slab and PSC I-Girder, Abutment, Piers along with Pile Foundation’ and the third is a ‘Set of Sample Editable CAD Drawings for the work. The drawings may be modified as per the design work and be submitted as required for the construction. The drawings are containing information on dimensions, structural detailing, bar-bending schedule, pre-stressing details and construction guides.

The Computer Applications for the design of Bridge Deck-Girders, Abutments, Piers and Pile Foundations are in AASHTO LRFD, are described in detail in the softcopy volume ‘User’s Guide for Hands-on Practice with Computer Applications’ for the book ‘Computer-Aided Bridge Engineering’ is available for download from web site ‘’.

The structural analysis of the grillage model is to provide the basic forces to be used in the design. Other considerations are used in the exhaustive design worksheet programs, the various design inputs may be altered by the user directly in the design Excel Worksheet for instant results with the altered design input data.

The grillage model is a finite element model by using three-dimensional beam elements. The deck-girder superstructure is defined as a lumped mass model, in which the relevant part of section properties and mass of the deck and girders are attributed to the surrounding beam elements. The boundary conditions with applicable restraints are defined as relevant to supports on which the grillage model is resting.

Commonly material properties are mentioned as a single material for the model. In a composite bridge, the material properties are different for steel and concrete, the orthotropic analysis gives more correct results.

The grillage model is subjected to Dead Load (DL), Super Imposed Dead Load (SIDL), and Live Loads for the moving vehicles. The applications of Live Loads are defined for various lane configurations and by following the applicable design standard.

The Load-Deflection stage analysis may also be carried out to get the non-linear effects of Loads on the grillage structure.

The basis of Design considers new concepts of Actions & their combinations that gives an idea about various design situation like persistent, transient, accidental or seismic combinations that might occur during the life of the structure. This will help bridge designers to design bridges for the worst loading situations.

The ULTIMATE LIMIT STATES is introduced in design standards these are 1. Limit state of equilibrium 2. Limit state of strength

The SERVICEABILITY LIMIT STATES deals on 1. Limit state of internal stress 2. Limit state of crack control 3. Limit state of crack control 4. Limit state of vibration 5. Limit states of fatigue.  However, the Limit state for vibration & the Limit state of fatigue are not covered i.e. specialized literature is suggested by the code.

The design in AASHTO LRFD Standard

For the design in AASHTO-LRFD, the Figures, tables, and equations are denoted by their home article number and an extension, for example, wherever they are cited. In early editions, when they were referenced in their home article or its commentary, these objects were identified only by the extension. For example, in Article, Eq. would simply have been called “Eq. 2.” The same convention applies to figures and tables. These objects are identified by their whole nomenclature throughout the text.

Please note that the AASHTO materials standards (starting with M or T) cited throughout the LRFD Specifications can be found in Standard Specifications for Transportation Materials and Methods of Sampling and Testing, adopted by the AASHTO Highway Subcommittee on Materials. The individual standards are also available as downloads on the AASHTO Bookstore,