A higher standard of bridge design

Staged Construction Analysis for Steel Bridges

to simplify the complicated and tedious modeling of complex steel structures while satisfying critical engineering issues such as checking girder local buckling, oil canning effect, and constructability check.

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**Issues in handling complex steel girder bridges’ staged construction analysis**

The steel plate girder bridge is one of the most popular and widely used bridge types. Although people often misunderstand it is easy to design due to its popularity, evaluation of the stability of steel members can be troublesome. In fact, bridge designers consider not only non-composite and composite but also long-term creep and shrinkage with the effective modular ratio of n. Primarily, modeling considering varying effective width or numerous section properties must be efficient. Even small configuration variations can easily more than double the number of stages, sections, and groups required. This can be a tedious process and results in human errors.

Therefore, bridge engineers need software that automatically calculates and considers section properties in each different sequences for accurate analysis results while complex layout and construction stage of the bridge is analyzed with simple steps user intuitively. Also, it is important that engineers should be able to build full 3D shell model easily or consider local buckling effect even using a grilled modeling approach.

**Process and features helpful for checking constructability of Steel Bridges**

**Significant Features and Differences in Results**

- 1. Reduce time to calculate section properties in sequence including:
- -Before Composite
- -After Composite
- -Compression Strength
- -Creep & Shrinkage

- 2. Increase efficiency to set up a bridge model with the complicated layout and various construction stages using Steel Composite Bridge Wizard.
- 3. Automatic calculation of member forces and stresses for steel girder and concrete deck separately and combined
- 4. Consider warping (local buckling) as the 7th DOF when girder is modeled using beam elements
- 5. Automatic conversion for resultant forces and stresses when girders are modeled using shell elements

**Negative Reaction (Uplift Reaction)**

The behaviors of the curved bridges, often used for the ramp or interchange, are very complicated. Special conditions like varying curve radius, steep skew angle, and irregular spacing of bearing result in higher negative reactions on the curved bridges. Engineers should be able to control the design variables such as the radius of curvature, skew angle, and spacing of bearings. In MIDAS, engineers can easily model and analyze a 3-dimensional model using the wizard or intuitive modeling methods.

**Deck pouring sequence**

In many cases, bridges can have different span to span ratios, continuous span, and deck pouring length and sequences. Those conditions result in varying stress of the deck. Engineers have to consider the deck pouring sequence appropriately to satisfy the constructibility limit state checking and longitudinal tensile stress limit in the concrete deck. Considering deck pouring sequences helps to control the crack in the continuous deck, tensile stress limit, and uplift reactions. Midas can check various cases of deck pouring sequence with different stages and deck length in each stage.

**Buckling Analysis**

Steel bridge design centers around solving and preventing buckling issues. for more detailed examination of buckling, plate elements are used to model girders, especially the web portion.

In buckling, there are a few critical variables such as the section material, the section stiffness, the slenderness ratio, and the boundary conditions of web and flanges. Therefore, it is important to simulate and evaluate various design scenarios using 3-dimensional Finite Element Analysis models.

**Vibration Control**

Steel bridges tend to be more vulnerable to vibration than concrete bridges due to its lighter self-weight. These vibration problems may not only affect the usability but also the possibility of resonance due to live load or earthquakes. MIDAS can perform analysis for sag and eigenvalue in 3D considering variables such as the slab thickness, span to depth ratio, etc.

**Bracing Modeling**

One of the most tedious tasks in steel bridge analysis is modeling the bracing members. Using MIDAS Steel Bridge wizard, engineers can model complicated bracing configuration in a simple manner - by defining geometric conditions such as spacings, gap, number per span, etc. instead of defining bracing members one by one according to their coordinate system.

**Resultant Force**

Curved or skewed girder bridges with composite steel plate girder are frequently simulated with plate and beam elements instead of beam elements with composite section. In case of modeling using plate elements or a combination of plate and beam elements, analysis results from multiple plate and/or beam elements should be converted to one member force for the design or rating code checking. Using the virtual beam and resultant force features in MIDAS, engineers can get resultant single member force automatically. These features allow engineers to review the resultant forces (Fx, Fy, Fz, Mx, My, and Mz) in a text/table/diagram format.

TESTIMONIAL

**Luis J. Vila at GM2 Associates**

**Atalay Yargicoglu at Stanley Consultants**

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