BRASS-GIRDER(LRFD) TM is a comprehensive system for the analysis and rating of highway bridge girders. BRASS-GIRDER(LRFD)TM uses Windows based Graphical User Interfaces (GUI) for data input. BRASS-GIRDER(LRFD)TM utilizes finite element theory of analysis and current AASHTO Load Resistance Factor Design (LRFD) specifications. Input and output may be created using English or SI Units. The program computes moments, shears, axial forces, deflections and rotations caused by dead loads, live loads, settlements and temperature changes. These actions are utilized by various subroutines to analyze user-specified sections of the girder.
Girder types may be simple span, continuous, hinged or cantilevered - with or without integral leg frame configuration. Girders may be constructed of steel, reinforced concrete or prestressed concrete (pre- and post-tensioned). Composite steel and composite prestressed concrete girders may be included.
BRASS can analyze variable depth girders, such as tapered or parabolic. The bridge configuration may be specified by limits of typical web depth variations, girder cross sections and bridge deck cross section. One important aspect of defining cross sections is the web depth, which is defined with a span profile rather than with the cross section. This is done because the web depth of the section may vary along the length of the span and independently of a cross section. This variation may be linear, parabolic, elliptic, or in steps. The cross section at any point along a span is a combination of the properties of the section and the web depth at that location.
The user may specify (by name) predefined cross sections that are stored in the cross section library. The library contains nearly all AISC rolled wide flange shapes and most AASHTO standard shapes for prestressed concrete I-beams. Using a library utility program, the user may modify the geometry of the existing sections, add new sections, or delete existing sections.
Stage construction may be modeled by respective cycles of the system for girder configuration and load application. Cycles are automatic if desired.
The dead load of structure members is automatically calculated if desired. Additional distributed loads and point loads may be applied in groups and each group assigned to a specific construction stage. Distributed loads may be uniform or tapered and divided into sections to model sequential slab pours. Loads due to prestressing are calculated and applied internally.
Live loads may be moving trucks or uniform lanes loads, which include the HL-93 vehicles described in the AASHTO LRFD specifications. A truck may have up to 24 axles. Up to 80 axles per truck may be input when using the SPECIAL-TRUCK command. Up to 10 trucks may be analyzed in one run. Impact may be user defined, as specified by AASHTO, or the user may reduce impact to model reduced speed limits.
Prestressed girder features:
- Simple span for dead load, continuous span for live load.
- Straight, harped or parabolic cable paths.
- Secondary moments due to creep and shrinkage.
- Stress relaxation of steel strand is accounted for as a function of time.
- Effects of temperature change can be analyzed at any stage.
- Support conditions can change from stage to stage.
- Results of individual loads may be obtained.
- Composite girders may be analyzed.
The BRASS input language allows the bridge engineer to communicate with the problem-solving capabilities of BRASS using terminology common to the bridge engineering profession. System input is free format consisting of commands grouped logically to define the bridge structure, loads to be applied and the output desired.