Dead Load Applications in Bridge Analysis Models

August 31, 2020
BLOG TIPS & TUTORIALS

Loading on structures can be idealized as static loads and are one of the major issues for structures. It makes permanent deformations to structures during the service period. The dead loads can be applied in the structural analysis as static loads. The static loads include nodal loads, distributed loads, and pressure loads in the structural analysis software. midas Civil also provides various load types to cover various loading conditions. In this webinar, we will examine how static load types are applied and which static load types are available.

 

The webinar contains short training for applying the Static Loads function in midas Civil. Furthermore, it introduces some application models to check how the Static Loads function is used. We recommend this webinar to beginners of midas Civil or engineers who are not familiar with FEM software.

 


This tutorial highlights:

 

1. Basic training for using static loadings


We will see load types in the Static Loads function of midas Civil, and also, take a look at demonstrations about frequently used types in Static Loads function.

 

2. Application models under static loading


We will see application models including static load types. While we take a look at example models, we will check how static load types are used to loading conditions.

 

3. Tips and advanced features


Static load types can be applied quickly. midas Civil has several options to speed up the user's tasks. This webinar will show some useful options. Moreover, we will have a look at additional options for advanced analysis.

 


 

What are dead loads?

 

Dead loads are one of the design loads in several design codes for structures and make permanent deformations to structures during the structures' service period. The weight of structures or attachments is a common case of a dead load. For instance, in a building, the weight roofs, walls, floors, columns, attachments, etc, can be considered dead loads. In bridges, the weight of girders, slabs or decks, piers, abutments, pavements, and other attachments can be considered as dead loads.

 

A building & a bridge
Fig. A building & a bridge

 

 


 

How to apply dead loads to an analysis model?

 

Analysis SW provides various load types that cover various loading conditions. midas Civil provides static loads function groups under the Load tab, including Self-weight, Nodal Loads, Beam Loads, and Pressure Loads function.

 

 

Various Functions in Node/Element Menu
Fig. Various Functions in Node/Element Menu

 

In order to define a load case, follow this procedure:

 

1. Click the Load tab.
2. Select Static Loads under the Load Type.
3. Click Static Load Cases and create a static load case.
4. Select a load type desired among the nodal nodes, beam loads, pressure loads.
5. Input values for loading and connect a load case.


 

Details of Each Function 

 

1. Static Load Cases function

 

Before we use each load function, we should define a load case via the Static Load Cases function. While running the analysis, the software will perform static analysis for each load case. When we define a load case, we should select a load type. There are many load types prepared in the function, but those are used when the autoload combinations functions which Auto Generation of Load Combinations in Load Combinations function is used. Therefore, if the user does not use the autoload combination feature, it is optional to select a load type. The user can select the User-Defined Load type or another function available.

 


Static Load Cases function
Fig. Static Load Cases function

 

 

 

2. Self-Weight function

 

Through this function, we can consider the weight of a structure easily. The self-weight is calculated with the volume of a structure, the weight density defined in material property, and the scale factor defined in this function. If the shape of a structure is not complex, we can compare analysis results and hand calculations.

 


Self Weight function
Fig. Self Weight function

 

 

 

3. Nodal Loads function

 

This function applies point loads to nodes of elements where available load types are axial forces and moments. The direction of loads follows the global coordinates system.

 

 

Nodal Loads function
Fig. Nodal Loads function

 

 

 

4. Beam Loads function

 

The Beam Loads function is subdivided into the Element Beam Loads function and the Line Beam Loads function. These functions apply point loads or distributed loads to beam elements. The Element Beam Loads function applies a load to each beam element. However, the Line Beam Loads function considers several beam elements as one element when loads are applied, as shown in the figure below.

 

Beam Loads function
Fig. Beam Loads function
Available load types function
Fig. Available load types function

 

Mainly, pressure loads can be applied through the Pressure Type function. Applied pressure loads are re-calculated as a uniformly distributed load considering the width or height of sections. Therefore, if pressure loads are provided as a design load and the users have beam elements as a model, users can use this function without additional calculation for input.

 

Pressure type in Beam & Line Loads function
Fig. Pressure type in Beam & Line Loads function

 

 

 

5. Pressure Loads function

 

This load type can be applied to plate elements and surfaces of solid elements. There are two ways to apply the pressure load:

 

1. Applying Pressure Loads with Define Pressure Load Type

The first way is to use the Define Pressure Load Type option. Here, we can define up to 8 load cases and apply all load cases to elements at once.

 

The procedure of applying pressure loads with Define Pressure Load Type
Fig. The procedure of applying pressure loads with Define Pressure Load Type

 

 

2. Applying Pressure Load without Define Pressure Load Type

The second way is to apply the pressure loads to elements directly. We select a type of pressure load and apply it to the elements selected.

 

The procedure of applying pressure loads with Define Pressure Load Type
Fig. The procedure of applying pressure loads without Define Pressure Load Type

 

 

6. Hydrostatic Pressure Loads function

 

Through the Hydrostatic Pressure Loads function, users can apply a Triangular shape or non-uniformly shape of pressure easier than the pressure loads function. This function can be used to consider the soil pressure or water pressure.

 

Hydrostatic Pressure Loads function
Fig. Hydrostatic Pressure Loads function

 

 

 

7. Plane Loads function

 

This function applies a load type defined in advance to the assigned plane. If there are elements in the assigned plane, the load will be placed on the elements. The important this is that the plane load type can be applied regardless of the mesh plan of elements.

 

Plane Loads function
Fig. Plane Loads function

 

 


 

Application Models under Static Loading

 

Now, let us see how the Static Loads group functions are applied to models in midas Civil.

 

1. Application models with Self-Weight function

 

Self-weight loads can be used in various structure models. The major reactions of structures against self-weight load show the deformation toward gravity, as shown in the figures.


Application models with Self-Weight function

2. Application models with Nodal Loads function

 

Nodal loads can be used to consider the weight of devices for construction. The devices could be a derrick crane, a lift crane, and a form traveler. For instance, in the figure below, the weight of form travelers and the eccentric loading of form travelers are considered nodal loads.

Application models with Nodal Loads function

Here, Nodal Loads are applied in the transverse analysis for a concrete box girder model.

 

The Nodal Loads function is used to consider the vertical component of prestressing force and wind load on the barrier.

Nodal load for the wind load & the vertical component of prestressing force

These example models are plate and solid models for a pier. Nodal loads are considered to apply the weight of the superstructure to the top of a pier.

 

Nodal load for the strut & tie model of the anchor pier

 

 

3. Application models with Beam/Line Element Loads function

 

In this example, beam loads are applied to grillage models for girder bridges. During construction stage analysis, beam loads are used to consider the weight of wet concrete for the slab on girders.

 

Weight of Wet Concrete

 

Here, beam loads are used to consider wind loads on bridges. 

Wind load on girders & an extradosed bridge

 

In these applications, beam loads are used to consider additional dead loads such as barriers, pavement, and other attachments. Additional dead loads can be applied individually to their location of a model or applied as total value.

 

Dead loads on an extradosed bridge & a CFT bridge

The next model is a culvert with beam loads. The culvert is modeled with beam elements. Therefore, beam loads are applied to consider external loading. The external loadings such as soil pressure, water pressure, and live loads are applied using the beam loads function.

 

the beam loads function.

 

 

4. Application models with Pressure/Hydrostatic Pressure/Plane Loads function

 

The last application models are examples of applying the Pressure, Hydrostatic pressure, and plane loads function. These example models consist of plate elements and solid elements. Pressure loads are used to consider the weight of pavement, barriers, and additional attachments.

 

Application models with PressureHydrostatic PressurePlane Loads function

 

These models are an integral bridge and a culvert that contains plate elements. Here, the Hydrostatic pressure loads function is used to consider soil pressure and water pressure.

 

 

Application models with PressureHydrostatic PressurePlane Loads function 2

 

The last model applies Plane loads function. This girder model has plate elements. When meshing this model, it does not consider loading location. Therefore, the plane loads function is used because plane loads can be applied regardless of node location.

 

Plane load (Area type) in a girder with plate elements

 


 

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TaeYong Yu | Technical Engineer | MIDASIT

Tae Yong is a bridge engineer within MIDASIT Technical Planning Team in South Korea. He has over 3 years of experience in the design of bridges and civil structures in Korea. He is familiar with international codes of practice including AASHTO, Eurocode and BS code. He has experience in discussing technical issues with engineers in Singapore, Malaysia, and Romania. From this webinar, he will share one of his experiences in Cable-stayed bridge design.

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