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**Modeling of Composite Steel Floors Using GT STRUDL**

Power Generation Engineering And Services Company Department of Civil Engineering Structural Design Central Group Modeling of Composite Steel Floors Using GT STRUDL A Presentation Submitted to: GT STRUDL Users Group 24th Annual Meeting & Training Seminar To Address Application of GT STRUDL for Structural Analysis of composite steel section February, 2012

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**Power Generation Engineering And Services Company**

PGESCo. PGESCo stands for (Power Generation Engineering Services Company) Established in 1994 Located in Cairo, Egypt Focused on EPCM (Engineering, Procurement, Construction and Management) Produced more than 20,000MW

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**Rendered View of a Combined Cycle Power Plant**

CTG / STG Add notes, Say 1- PGESCO main design activity 2- PGESCo is an engineering firm located in Cairo, Egypt. CTG ( Combustion Turbine Generator)/ STG (Steam turbine Generator) 3

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**Structures in power plants where composite slabs are used:**

Steam Turbine Generator “STG” Building. Combustion Turbine Generator “CTG” Building. Control building. Electrical building. Circulating Water Electrical Building “CWEB”.

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**Control building during construction:**

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**Control building model using Gtstrudl:**

Model include structural steel upper part and the concrete lower part (Walls and Slab) -Concrete slab is represented by big horizontal X brace to simulate rigid diaphragm action. The purpose of this study is how to model the slab as a diaphragm and a support for gravity loads. Model include structural steel upper part and the lower concrete part (Walls and slab). The question is there any accurate model rather than the big horizontal brace?? 6

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**Models used to simulate Composite Steel Floor**

1- Full model 2- Springs were used to replace beams to control deflection 3- Plate elements were deleted at corners only. 4- Plate elements on the girders were deleted to insure floor was not spanning between girders. 5- Element has one direction 6- Sequential analysis 7- Rigid element between beam & slab 8- Master & Slave 9- Eccentricity between the centerline of plate and steel beams. 7

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**Criteria for the normally used design model.**

Bending moments in the slab, approach approximate values obtained using continuous beam analysis results (confirm one way action), Bending moments in beams (confirm transverse beams support of the concrete slab) Bending moment in the Girders (Confirm Girders support of the transverse beams). Lateral deflection ( Confirm rigid diaphragm action by the concrete slab) The above 4 limits will be compared with a MANUAL calculation A simpler structure than the control building will be used for this case study. 8

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**Simple structure: Slab thickness 200mm**

Gravity Load 1.0 metric tons/m2 (200psf) Lateral Load metric tons (22.0 kips) Hinged supports at column bases. 9

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Manual Calculation: Girder Column Filler beam 10

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Manual Calculation: For Concrete Slab:- 11

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**Manual Calculation: For steel filler beams:-**

The steel (filler) beams behave simply supported on steel girders. Steel beam span (L) = 10.0 meters. Beam uniform load (w) = slab uniform load * spacing =1*2 = 2.0 t/m’ Maximum bending moment (M)=2*102/8= 25 m.t (180.8Kip.ft) Maximum deflection (Δ) = [5*(2*(1000)4]/[(384*2100*35088)] = 3.53 cm = 35.3 mm (1.39in) Reaction =2*10/2=10ton (22.04Kip) 12

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**Manual Calculation: For steel girders:-**

The steel girders behave simply supported on steel columns. Steel beam span (L) = 10.0 meters. Steel girder loads are the reaction of filler beams Maximum bending moment M=0.6*10*10=60 m.t (433.9 kip.ft) Maximum deflection (Δ) = [(0.063*10*(1000)3]/[(2100*56191)] = 5.34 cm = 53.4 mm (2.1in) Reaction=4*10/2=20 ton (44.1 kip.ft) 13

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**1-Full model used: 10m X 10m X 6m high structure.**

Braced in one direction & frame action in the other. Columns W10X33, and vertical brace WT5X11 Girder size of W24X55, and transverse beams size of W21X44 Slab thickness 200mm supported by the steel filler beams. Gravity Load 1.0 metric tons/m2 (200psf) Lateral Load metric tons (22.0 kips) Hinged supports at column bases. 14

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**1-Full model used: Bending in filler beams & girders uniformly loaded**

- Hand calculations: Bending moment in the filler beams = 25 m.t and in the girders equal to the 60m.t which is not equal to the output from the full model. Explain? - The outer beams carry more than the inner filler beam which is not consistent with one way action of a slab……. This is consistent with the following slide that shows the outer beams supporting the slab, while the inner beams are partly supported by the slab. It also represent the two way action by the slab. 15

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**1-Full model used: Bending in slab (Neg. mom.= 0.0)**

One way action does NOT exist Explain? 16

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**1-Full model used: Displacement at joints in mm under Load 1**

Seems like slab is supporting the filler beams. Hand Calculation shows filler beam max deflection = 35.3 mm (1.39 in) 1-Displacements are not equal 2- They are not equal to the manual calculation which is 35.3mm. 3- No deflection reversal. 17

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1-Full model used: GT results are quite different from the results obtained by the manual calculation because of the combined action of the slab and the steel beams. Each of the upcoming trials has its own perspective in choosing the methodology to represent the composite action of floor beams. Each model presented a different set of problems simulating composite action. A comparison of the results will be made with manual calculation. The results will be evaluated to understand the reasons for differences of the results from those of manual calculations. 18

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**2-Springs used to control deflection**

Solve the beam manually for uniform load W obtained by multiplying the area uniform load by beam spacing Calculate the deflection @ 0.5m intervals(0.5m X 0.5m Plate elements) Multiply the uniform load by 0.5m to get concentrated load Divide the concentrated load by the deflection calculated manually at this point to get stiffness 19

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**2-Springs used to control deflection**

This stiffness used represents the steel beam. In the model the steel beams are replaced by the calculated spring constants. This model cannot be used simply because the added springs generate vertical reactions that are not transmitted to the columns which generate lower reaction loads at the columns. 20

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**3-Delete plates at corners only**

Delete elements at the corners to prevent the slab from being directly supported by the columns 21

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**3-Delete plates at corners only**

Bending moment in the steel beam 22

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**3-Delete plates at corners only**

Bending moment in the slab 23

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**4- Delete plate elements on the girders**

Delete the plate elements that rest on the girder to force the slab to transfer the load to the beams then to the girders then to the columns 24

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**4- Delete plate elements on the girders**

Bending moment in the steel beams 25

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**4- Delete plate elements on the girders**

Bending moment in the slab 26

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**4- Delete plate elements on the girders**

Vertical displacement 27

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**5- Element has one direction of distribution**

PSRR element type are used in modeling The problem that the PSRR elements do not permit the consideration of bending stiffness analysis nor the dynamic analysis 28

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6-Sequential analysis A thought was discussed that the sequential analysis will get GTS to differentiate between the stage when the concrete is wet and the next stage when the concrete hardens. This approach was not what was thought to be and hence, it was abandoned. 29

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**7- Rigid elements between beam and slab**

This modeling technique did not produce a good representation of the bending moment which can not be explained. 30

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**8- Use of Master and Slave Joints**

This also did not produce a good representation of the bending moment. 31

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**9- Eccentricity Eccentric between the steel member and**

the concrete plate elements 32

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**9- Eccentricity Weird Bending moment diagram which had no explanation.**

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**9- Eccentricity Bending in the slab 34**

But at this step we are confidante that the modeling the concrete above the steel or using the eccentric option is the almost right way to model the composite action but still need a lot of enhancement 34

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**Models used to simulate hand calc till now**

1-Full model 2-Springs were used to replace beams to control deflection 3-Plate elements were deleted at corners only. 4-Plate elements on the girders were deleted to insure floor was not spanning between girders. 5- Element has one direction 6- Sequential analysis 7- Rigid element between beam & slab 8- Master & Slave 9-Eccentricity between the centerline of plate and steel beams. Place this slide before the full model slide. 35

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What to do next??? None of the above modeling techniques produced a good representation of the approximate manual approach. So a combination of the above modeling techniques will be tried to reach a reasonable representation of the structure with some modification It was suggested to use a combination of the eccentric modeling approach together with the deleted elements at the corners for: Easy to model “applicable for every day work” Actual representation of the differences between the steel beam CL and the concrete slab CL. The modification will be by varying one of the following parameters Thickness of the slab Young's Modules of the concrete slab This will be deleted. For organization purposes only. 36

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**Variation in Thickness for the slab**

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**Variation in Thickness for the slab**

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**Variation in E for concrete**

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**Variation in E for concrete**

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**Variation in E for concrete**

Bending moment in the steel beam Case = 0.25% E 41

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**Variation in E for concrete**

Bending moment in the slab Case= 0.25% E 42

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**Variation in E for concrete**

Lateral difflection in Z direction (Braced Dir.) Adjust note as follows: Load 2. Displacement at joints, mm. Add also inches. 43

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**Variation in E for concrete**

Lateral deflection in X direction (Moment frame dir.) 44

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**Verification – Other Software**

Comparing results to those obtained by using another software an other program with a composite beam module built in 45

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**Verification – Other software**

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Conclusion Using the Eccentric model with the deleted shell element at the corner with a reduction in the E of the concrete slab, produces results in agreement with the manual calculations. The following table summarize these results. 47

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**Questions and Discussion**

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