GP RM E Composite Steel Concrete AASHTO

RM Bridge Professional Engineering Software for Bridges of all Types

RM Bridge V8i

October 2010

TRAINING COMPOSITE STEEL-CONCRETE -MODELER + RM - AASHTO

RM Bridge

TRAINING COMPOSITE STEEL-CONCRETE -MODELER + RM - AASHTO I

© Bentley Systems Austria

Contents

1 General ......................................................................................................................... 1-1

1.1 Introduction.......................................................................................................... 1-1

1.2 General Remarks ................................................................................................. 1-1

1.3 Example ............................................................................................................... 1-2

2 Input Modeler ............................................................................................................ 2-1

2.1 Axis Definition .................................................................................................... 2-1

2.2 Cross-Section definition ...................................................................................... 2-1

2.2.1 Cross-Section Geometry .................................................................................. 2-1

2.2.2 Cross-Section Part Allocation.......................................................................... 2-2

2.2.3 Reference Set Definition.................................................................................. 2-5

2.3 Segment Definition .............................................................................................. 2-6

2.4 Export to RM ..................................................................................................... 2-10

3 Input RM...................................................................................................................... 3-1

3.1 Introduction.......................................................................................................... 3-1

3.2 Shear Studs .......................................................................................................... 3-1

3.3 Load Input ............................................................................................................ 3-3

3.4 Construction Stages ............................................................................................. 3-5

3.4.1 Activation ........................................................................................................ 3-5

3.4.2 Calculation Actions ......................................................................................... 3-6

3.5 Post-Processing .................................................................................................... 3-6

3.6 Cracked Tensile Zone ........................................................................................ 3-11

3.6.1 General ........................................................................................................... 3-11

3.6.2 No Tension Elements ..................................................................................... 3-12

RM Bridge

TRAINING COMPOSITE STEEL-CONCRETE -MODELER + RM - AASHTO II


3.6.3 Reload Option ................................................................................................ 3-13

RM Bridge

TRAINING COMPOSITE STEEL-CONCRETE -MODELER + RM - AASHTO 1-1


1 General

1.1 Introduction

This document was prepared with the intention to demonstrate the procedures and

principles implemented in RM for the analysis and the design of composite bridge

structures. A simple example of a composite two-span beam will be used for this purpose.

The present document is based on the assumption that the reader has a basic understanding

of the software. Only input procedures specific for the purpose of explaining the input of

composite structures will be explained in detail.

1.2 General Remarks

A composite structure in the context of RM is any structure with cross-sections composed

of multiple parts. Each part can be made from an individual material and can be activated at

an individual time. Therefore, the definition is quite general and includes for example steel

I-beams or troughs with concrete slabs, pre-cast concrete beams with cast-in-place concrete

slabs, etc.

The concept for the analysis of composite structures in RM is based on the assumption that

partial elements are combined to form composite elements. Each part of the composite

element (steel girder, concrete slab etc.) has to be defined as a separate partial element, and

the related cross-section parts have to be assigned to the start and endpoints of these

elements. A separate composite element has to be defined for every combination of partial

elements. The composite cross-section of these elements is automatically created by

combining the cross-sections of the partial elements (Figure 1). For the composite cross-

section a reference material (ER) must be given with which an equivalent stiffness can be

computed.

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part1 = steel I-beam

part2 = concrete slab

part3 = composite

beam (= parts 1+2)

11AE

22 AE

RE

AEAEA 2211

3

Figure 1. Composite beam consisting of three cross-section parts.

1.3 Example

Consider the two-span continuous beam documented in Figure 2. Structural system for the

given example. It will be assumed that the steel I-girder is erected in a first construction

step. Self weight of the steel girder and the weight of the wet concrete slab are applied on

the steel girder. Once the concrete has hardened composite action can be activated. An

additional dead load of 5kN/m is then applied on the resulting composite system to finalise

the construction stages. All permanent loads up to this stage will be accumulated in load

case LC1000. Additionally, a simple traffic load of a centrally positioned concentrated load

will be applied. The traffic load is not intended to be in accordance with the AASHTO

code. Results for the traffic loading will be stored in a superposition file called Traffic.sup.

The node and element numbering scheme for this example is given in Table 1.

cross-section

0.4m

0.8m

0.7m

2.4m

20mm

100mm

30mm

0.5m

15m 15m

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Figure 2. Structural system for the given example.

Table 1: Structural system for the given example

Component Element # Node #

Steel I-beam 101-130 101…

Concrete slab 201-230 101…

Composite beam 301-330 101…

Support springs 1101, 1201, 1301 101, 116, 131

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2 Input Modeler

2.1 Axis Definition

No specific requirements exist for the definition of the axis for the given

structure. The usual procedures to define a straight axis of 30m length in

plan and elevation view can be performed. The axis will be stored under

the name axis1.

2.2 Cross-Section definition

2.2.1 Cross-Section Geometry

The cross-section as shown in Figure 2. Structural system for the given example. will be

defined in the following steps. A cross-section object called cross1 needs to be created.

As with all other cross-

section types, the input of

a composite cross-section

is based on construction

lines. The construction

lines shown beside need to

be generated for this

example.

Parallel lines at 0.01, 0.25, 0.35, 1.2

meters in both directions.

Parallel lines at 0.4, 0.43,

1.1, 1.2 meters.

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Cross-section elements can

now be defined as shown

beside.

2.2.2 Cross-Section Part Allocation

Each element must now be assigned to the correct cross-section part number. In the present

example the steel component will be part 1, the concrete component will be part 2 and the

composite section will be part 3.

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Cross-section parts are managed through the parts

management window at the bottom of the screen. By

clicking the little arrow next to Part: 1 the parts

management window can be accessed. Part 1 is added

automatically when a cross-section is started. Additional

parts can be added by editing this list in the usual way.

For every new part a reference point must be specified.

This reference point later becomes the structural node for

the element series for this particular part. Very often the

reference point for all parts forming a composite beam will

coincide (In this example part 1, 2 and 3 are on the top of

the concrete slab).

For the present example three parts need to be initialised.

Part 3 must be defined as the composite part consisting of

parts 1 and 2. The definition of the composite part can be

activated by editing part 3 in the parts management

window and selecting parts 1 and 2 as the composite parts

from the drop down menus.

After entering the described definitions part 2 should be

activated in the parts management window.

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After pressing the assign element to active part button shown on the left,

individual elements can be assigned to the active part. The active part is

displayed in the small parts window at the bottom of the screen and should be

“2” in the present situation. Clicking into an element changes the part number

to the active part number.

All elements of

the concrete

slab should now

be assigned to

part 2 by

clicking near

the position of

the part

number. It is

assigned to part

2 when there is

a “2” in the

middle of the

element.

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2.2.3 Reference Set Definition

Various points in the cross-section need to be

identified for later use. These points must be

collected in so-called reference sets. For the

given example three reference sets will be

generated: one reference set called connection

for a connection point identifying the location

of support conditions and two more reference

sets called ssig and csig for the identification of

stress points in the concrete and in the steel part

respectively.

The RefSet management window can be reached

by clicking on the little arrow next to the RefSet

window at the bottom of the screen. The RefSet

input screen is reached by adding a line to the

list. The input necessary to define the three

reference sets is shown to the left. Note that all

reference sets are associated with a particular

cross-section part. For this reason, the stress

check points do not need a material assigned.

When a material is assigned to a part, all stress

check points assigned to that part will assume

the material.

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The icon can be used to define the desired

reference points. The connection point should

be defined at the bottom of the cross-section in

the centre of the steel flange. The stress points

should be placed on the bottom and top of parts

1 and 2 respectively and should be called

csig_top, csig_mid, csig_bot, ssig_top and

ssig_bot as shown in the picture beside. When

placing a stress point, make sure that the correct

Ref. set is active and displayed at the bottom of

the screen, and the correct part is active and

displayed at the bottom of the screen. Ssig is

for steel stress check points (part 1), and csig is

concrete stress check points (part 2).

2.3 Segment Definition

Double click on Segments in the menu tree to define a new segment. A new segment

called seg1 should be added here. Default settings are adequate for the purpose of the

present example.

For the present

example 31 segment

points with an

increment of 1

meter should be

defined. The cross-

section should be

cross1 for all

segment points.

Element series can

now be defined for

each part by

clicking the circled

icon.

csig_top csig_mid

csig_bot

ssig_top

ssig_bot

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Highlight part 1 in the segment point list, click the edit

icon and enter the information as shown to the left to

define the steel elements of the beam.



define the concrete elements of the beam.

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define the composite elements of the beam. Note that

concrete _C7ksi will be used as the reference material for

the composite section.

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The newly assigned

elements are now

also visualised in

the segment points

window. On the

connection tab the

three support

conditions can be

defined at segment

points 1, 16 and 31

(begin, midspan,

end). Highlight

point 1, and on the

Connections tab

select “insert after”,

then Spring-0.

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Use the following input values to define the three spring-0 elements:

2.4 Export to RM

This concludes the definition of the composite structural system using the

Modeler. The system is now complete and available for export to RM.

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3 Input RM

3.1 Introduction

Upon entering RM the structural system is displayed in the default view setting as shown in

Figure 3 a. After recalculating with a cross-section calculation and structure check, the

cross-section properties have been computed and the system can be displayed as shown in

Figure 3 b and c depending on the visualisation settings.

(a)

(b)

(c)

Figure 3. Structural system before and after recalc after export from GP.

3.2 Shear Studs

Special shear stud spring elements are available for composite cross-sections in RM (Figure

4). These shear stud elements must be defined as spring elements by the user connecting the

same structural nodes as the associated composite elements. Their number, by default, must

be the number of the elements formed by the first cross-section part plus 10000. In this

example, that means the first shear stud will have element number 101 + 10000 = 10101.

For these elements no other information needs to be defined; the warnings regarding the

missing spring stiffness during calculation can be ignored. These shear stud elements do not

contribute to the structural stiffness of the system. However, the change in normal force per

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length within this element is stored and can be accessed during post-processing. During

result superposition, results for these elements are added together as for the other structural

elements in the system, ensuring that the true minimum and maximum values for the shear

force are computed. For the present example spring elements 10101 to 10130 need to be

defined.

Nc,1

Ns,1

Nc,2

Ns,2

M1 M2 shear stud element (#10107)

#107

#207

composite element (#307)

Figure 4. Composite and shear stud elements with element numbers.

The spring elements modelling the shear studs can be input

under Structure – Elements – Element Types and Nodes.

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Select “insert after” in the window showing all other

elements already. The input defining the shear studs is

shown on left.

3.3 Load Input

Loading information will be defined in the next few input steps. Three load cases will be

defined: self weight of the steel girder (LC101a), weight of wet concrete (LC101b) and

additional dead load on the completed structure (LC201). Additionally a simple traffic load

will be defined. LC101a and LC101b will be accumulated in LC100 and LC1000 and

LC201 will also be added to LC1000 and LC200. The input sequence in the load manager

should produce a listing as shown below.

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The input for LC101a containing the

load information for self weight of

the steel girder is shown on the left.

The loading will be applied on

elements 101 to 130 which have

been assigned to the steel cross-

section part. If Gamma is 0.0 RM

takes from the material table the

respective value for the unit weight

of the assigned material.

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The input for LC101b containing the load exerted

by the wet concrete slab onto the steel girder is

shown on the left. Note that the loading acts on

elements 101 to 130. Since the specific weight of

the concrete is 25kN/m3 and the cross-section

area of the concrete slab is 0.96m2 the load can be

computed at 24kN/m.

The input for LC201 containing the additional

dead load of 50kN on the composite structure is

shown on the left. Note that this load is applied

on elements 301 to 330 which is the element

series for the composite system.

In addition to the loads above, a traffic lane in the

centre of the composite beam (Macro1, elements

301 to 330) and a simple load train consisting of a

single concentrated load of 200kN needs to be

applied. Note that the Free length tick box must

be un-ticked for the load train definition.

3.4 Construction Stages

3.4.1 Activation

Four stages will be defined for this example. In the first stage elements 101 to 130 (steel

beam) and 1101, 1201 and 1301 (support springs) are activated. In the second stage

elements 201 to 230 (concrete slab), elements 301 to 330 (composite beam) and elements

10101 to 10130 (shear stud elements) should be activated. A traffic load evaluation will be

performed in the third stage and post-processing will be performed in stage four. No

elements need to be activated in stages three and four.

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3.4.2 Calculation Actions

stage1:

In stage 1 self weight of the

steel beam (LC101a) and

loading of the steel beam due to

the weight of the wet concrete

slab (LC101b) will be applied.

Some administrative actions

also need to be called in stage

one as is shown on the left.

stage 2:

In stage 2 additional dead load

(LC201) will be applied.

stage 3:

In stage 3 a simple traffic load

evaluation as shown on the left

should be defined.

3.5 Post-Processing

The existing example can now be calculated (Recalc). If no error messages or warnings

appear the calculation run has been successful and results are available for post-processing.

Depending on the particular situation it is necessary to obtain results either for the complete

composite section or for each part. In all post-processing situations within RM options can

be selected to facilitate the choice of result type. Options are usually named normal, joined,

split or joined/split. These options are only available for normal forces and bending

moments and have the following meaning:

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Normal. The results for the selected elements

and load cases will be displayed as they are

accumulated for each particular element.

Joined. The results will be displayed for the

selected composite cross-section. Results

components which have originally been

computed for parts of the cross-section will be

joined.

Split. The results will be displayed for the

selected cross-section part. Result components

which have originally been computed for the

full composite cross-section will be split as

shown in.

Joined/Split. The software determines which

option is used and suggests an appropriate

default.

Post-processing for this

training example will

be performed using

RmSets. In order to

define these RmSets

the RmSet management

window should be

opened (Properties –

RmSets).

A first RmSet for the

visualisation of the

bending moment in the

steel girder due to

permanent loading

called steel_pl_Mz

should now be created.

By clicking on the Info-

button in the lower

table the contents of

this particular RmSet

can be defined in the

input screen shown in

Figure 5. Input screen

for RmSets below.

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Figure 5. Input screen for RmSets

element selection:

Elements associated with an

RmSet can be selected by

clicking on the circled Elements

and Nodes button in Figure 5.

With the help of this RmSet the

bending moments in the steel

girder due to permanent loading

will be visualised. Therefore

elements of a group - steel need

to be selected and added to the

list by pressing the “insert

before” button as shown on the

left.

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result file selection

The source of the results will be the

summation file for permanent load case

results LC1000. By clicking on the circled

Load Cases button in Figure 5. the input

screen for the specification of results in

this RmSet can be reached. Since

permanent loads act partly on the steel

girder only (LC101a and LC101b) and

partly on the complete composite system

(LC201) it must be specified that the result

components for the steel be only need to

be determined. This is specified by

clicking the split tick box as shown on the

left.

Finally, the result component needs to be

chosen, in this case, Mz. This newly

specified RmSet can be stored now for

later reference in the construction

schedule. An immediate check of its

functionality can be performed by clicking

the Plot diagram button.

Similar RmSets can now be created for

bending moments and normal forces in the

steel and concrete parts as well as in the

full composite section. For the composite

section the joined button must be ticked

since the accumulated results on the full

section will be of interest. The same can

be done for the traffic load envelope

traffic.sup. Stresses can also be plotted by

selecting the appropriate Stress points

after ticking the check box for Stress.

Results for the shear studs are obtained by

creating an RmSet for elements 10101 to

10130 and visualising the normal force.

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If all RmSets as outlined above are

generated then the list of available RmSets

should look like the list shown on the left.

stage 4:

Selected RmSets can now be used for

automatic post-processing in stage 4 of the

construction schedule as shown on the

left.

Alternatively, this output can be viewed

interactively in the Results-Plot-Rm Sets

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3.6 Cracked Tensile Zone

3.6.1 General

In the design of composite multi-span bridges the consideration of cracked tensile zones in

reinforced concrete components is an important issue. Several methods of taking cracked

concrete zones into account are implemented in RM:

Computation of the structural response using linear elastic theory and the full

composite cross-sections. Based on these results, redistribution of results can be

computed for each cross-section based on material properties.

Usage of a structural model without concrete components in tensile zones.

Modelling of the full composite structure and definition of the applicable material

properties for each of the components used. The material non-linearities can then be

taken into account when computing the structural response.

For this training example, the first option will be demonstrated. After redistribution of the

forces for the composite section, forces must be the same as before this operation whereas

the stress distribution in the individual components of the cross-section will be different.

While this method is elegant because it can be performed on a complete composite system

and can be based on a linear-elastic analysis it has a number of draw-backs that must be

carefully considered when applying this procedure:

The redistribution is only performed on a cross-section level and no repercussions

on the global stiffness of the structure are taken into account.

Redistribution of the result vector can be defined in a consistent manner only in

certain cases where the cross-section axes of each part and also of the composite

section are aligned with the global axis, where shear lag is not considered etc.

The additional stiffness provided by the reinforcement is not considered.

Shear stresses cannot be redistributed in this manner.

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3.6.2 No Tension Elements

In a first step the elements which

cannot receive tensile stresses must be

identified. This is done in the input

pad reached via Structure – Element–

Checks.

The concrete elements 201 to 230

need to be defined as no tension

elements.

In the implemented stress

redistribution procedure it is checked

whether tensile stresses are present in

the centre of gravity of these no

tension elements. If this is the case

then normal forces are redistributed to

other cross-section parts. The

redistribution is performed in such a

way that the joined result for the

composite cross-section remains the

same.

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3.6.3 Reload Option

stage 5

The Reload action has been

implemented for the purpose of result

redistribution on a cross-section level.

In a fifth construction stage the two

commands ReloadLc and ReloadSup

need to be inserted for the permanent

load summation load case LC1000

and the traffic load envelope

traffic.sup respectively. Plotting the

stresses for the centre of the concrete

part illustrates the effects of the

Reload action.(e.g. stress; csig_top)

Redistribution, no

tensil force

Documents

GP RM E Composite Steel Concrete AASHTO