Overview

The general philosophy governing the design of bridges is that, subject to a set of loading rules and constraints, the worst effects due to load application should be established and designed against. The process of load application can be complex as governing rules can impose interdependent parameters such as loaded length on a lane, lane factors, and load intensity. To obtain the maximum design effects, engineers have to try many loading situations on a trial and error basis.

This leads to the generation of many live load application instances (and a large volume of output data) that then must be combined with dead load and other effects, as well. Bridge Deck is used to minimize the load application process while complying with national code requirements.

The program is based on the use of influence surfaces, which are generated by STAAD.Pro as part of the loading process. An influence surface for a given effect on a bridge deck relates its value to movement of a unit load over the point of interest. The influence surface is a three-dimensional form of an influence line for a single member (or, in other words, it is a 2D influence function).

STAAD.Pro will automatically generate influence surfaces for effects such as bending moments for elements, deflection in all the degrees of freedom of nodes, and support reactions. You then instruct the program to utilize the relevant influence surfaces and, with due regards to code requirements, optimize load positions to obtain the maximum desired effects.

Once the influence surfaces have been generated, they are saved and can be reused for any further investigation that may be required. These remain valid as long as the you do not altered the structural model. Changes to the structural model can alter the pattern of the influence surfaces and you must ensure that a further analysis takes place before any further processing.

Your engineering knowledge and judgement is critical in deciding which effects are required and at what position to obtain them. This is where you can save a lot of processing time and also can ensure critical positions are not missed.

Bridge Standards

The Bridge Deck mode supports the following standards:

• UK: BS 5400 Part 2
• UK: BD21/01 Chapter 5 and Annex D
• American: AASHTO ASD/LFD
• American: AASHTO LRFD
• Indian: IRC Chapter 6

All the relevant code instructions for loading definitions and traffic lane calculations are incorporated in BEAVA and, in cases where vehicle axle arrangements are not standard, it is possible to define a vehicle and save it in the library for use it in the analysis.

BEAVA is fully integrated in STAAD.Pro and utilizes the same GUI for all input and output data.

Roadway and Load Modeling

You must define the width of the Roadway as straight or curved parallel lines. BEAVA then automatically calculates the following in accordance with the selected code:

• Number of Notional Lanes (Traffic Lanes)
• Influence lines along the center line of notional lanes
• Loaded length along the Lanes
• Critical location of uniformly distributed load
• Critical location of knife edge load
• Critical location of vehicle load
• Maximum effect value
• Associates effects values

Once the program has completed calculating the above, a text file containing the results is displayed on the screen.You can also then examine the results graphically.

Loading arrangements for the effects requested can be displayed on the model and, for every loading arrangement produced, you can instruct the program to generate a STAAD.Pro load case. The added live load cases can be combined with dead loads using the normal STAAD.Pro load combination generation. The final model can then be analyzed in STAAD.Pro and then post-processed.