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Superstructure Design of Warren Truss Bridge with the LRFD Method
Donald Essen, Riyan Ambara, Syafwandi, Resi Aseanto Faculty of Civil Engineering Mercu Buana University Jakarta, Indonesia [email protected], [email protected], [email protected],
[email protected]
Abstrak
A bridge is a structure built to span an obstacle such as a river, valley, road, or rail. In the world of construction, there are various types of bridges that are used to connect a road, one of which is a steel truss bridge. Based on the type of structure, truss bridges also have many types. In this study, the bridge is planned to be reviewed on the superstructure only. Planning is carried out using a warren truss bridge using the LRFD method based on the loading regulations in SNI 1725-2016 and AASHTO LRFD Bridge Design Specifications 2017. Steel profile analysis using RSNI-03-2005 and SNI 1729-2020. The author planned this bridge in the 3D model using SAP2000 v20 software.The results of the structural analysis of factored loads, overall for the truss bridge is safe to withstand the working load by using the profile WF350.350.12.19 for the top chord, bottom chord, and diagonal truss. The value of the bridge deflection caused by the load is still below the maximum allowable deflection. The gusset plate is designed using a Whitmore section method.
Keywords
Gusset Plate, Steel Bridge, Warren Truss, Whitmore Section
1. Introduction
The phenomenon of flooding due to the overflow of the Cileungsi River in the rainy season resulted in the interruption of existing roads and bridges due to being flooded, so that alternative routes were needed in other locations on higher ground. Planning for the bridge construction between Cikiwul Village, Bekasi City with Bojong Kulur Village, Bogor Regency crossing the Cileungsi river will replace the existing temporary wooden bridge.
Based on bridge span requirements and referring to the standards of the General Guidelines for Economic Spans of Bridges, the superstructure bridge is planned using the steel truss. The steel truss bridge is a structure consisting of a series of steels connected to each other. The load will be distributed and transmitted to each truss element as compressive and tensile forces through the connection points. In this case the steel truss bridge is a solution to overcome the tensile and compressive forces that arise in the bridge structure, especially in structures with large spans. steel trusses used for building bridges are considered. Steel has higher strength, ductility and toughness than many other structural materials such as concrete or wood. However, steel must be painted to prevent rusting (Sharma & Pahwa, 2018). The warren truss type was chosen in this study because it has safety, comfort, and a lighter load than other types of a bridge (Purwanto & Hariadi, 2018).
This study aims to provide an alternative design for the upper structure of the bridge in Bojong Kulur using a warren truss type using the LRFD (Load Resistance Factor Design) method, so that it is expected to provide benefits for the Civil Engineering and education in general. To achieve this goal, the following research objectives are defined:
1. Produce a structural design of warren truss bridge in accordance with the specified requirements.
2. Measuring the dimensions of steel profiles used in the design of steel truss bridges.
3. Determine a detail of the steel truss connection
2. Research Methodology
A plan must be carried out in a clear and orderly manner so that the results can be accounted for. This analysis process requires software to design a bridge. Csi SAP2000 software is used to get the reference of the forces on the axial force (Pu) and moment (Mu). Then we use the Microsoft Excel software to get into the literacy related calculations. The description and design methodology of the steel frame bridge structure can be explained as follows:
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2.1. Process Data
General data:
Total span : 40 m
Truss height : 6.3m (taking into account clearance against vehicle height) Vehicle Floor Width : 6 m
Sidewalk Width : 0.5m
Cross Girder Spacing : 5 m Stringers Spacing : 1.50 m Thickness of Concrete Slab : 0.2m
2.2 Research Flowchart
2.3.Data Analysis Techniques
This research is divided into several steps as follows:
1. Step I
Preparation phase. Preparations were made to find data and information that support bridge planning.
2. Step II
Determine the layout and dimensions of the bridge.
Star t
Data collection and literature:
Regulation the bridge standard & code Books related to bridges Primary data & secondary data
Bridge Planning:
Determine the bridge layout Define dimensions
Determination loading of the superstructure:
Dead load Live load Environmental load Preliminary design:
Design of truss bridge superstructure components using Csi SAP2000
Structural Analysis
NO Control strength,
tension and the deflection of the
superstructure YES Connection Planning
Finish
Drawing of Planning Results
39 3. Step III
Determination of the loads on the superstructure of the bridge.
4. Step IV
Preliminary selection of steel profiles for the main elements of the bridge superstructure.
5. Step V
Structural analysis of the structural model with the help of the SAP2000 Structural Software to determine the compressive or tensile forces and moment on the structure bridge against the working loads.
6. Step VI
Control of steel profiles against compressive or tensile forces obtained from the results of structural modeling from the SAP2000 software.
7. Step VII
Determine the design of the truss connections.
8. Step VIII
Conclusion. Based on the results of the analysis and discussion, a conclusion is made per the research objectives
3. Observations of Design Process 3.1. Building Planning Data
Figure 1. Steel Truss Schematic Material of Steel : SM490
Fy : 345 Mpa
Fu : 490 Mpa
E : 200,000 Mpa
Material of Concrete : K350
Fc' : 30 Mpa
Ec : 4700 MPa√
3.2 Load Factor and Load Combination
The loading that works on the highway bridges refers to SNI 1725-2016 and AASHTO LRFD Steel Bridge Design Specification. The value of the load obtained is then inputted to each bridge structure on the SAP2000 software according to its placement.
3.2.1. Permanent Dead Load (MS)
In this plan, self-weight is analyzed automatically with SAP2000 software.
3.2.2. Additional Dead Load (MA)
Table 1. Dead Load Recapitulation
No. Additional Dead Load Type Thickness (m) Density (kN/m3) W(kN/m2)
1 Asphalt & overlay 0.1 22 22
2 Railing (Ø3 inches) 0.275 0.275
3 Water/Rain 0.05 10 0.5
4 Sidewalk 0.25 24 3
Q DL on bridge floor 5,975
Source: Data in Research, 2021 5 m
40 m
6.3 m
40
3.2.3. Live Load (LL)
Table 2. Live Load Recapitulation
No Live Load Load
1 Lane Load (TD) 7,875 kN/m2 2 Concentrated Line Load 49 kN/m 3 Dynamic Load Factor 19.6 kN/m 4 Braking Force (TB) 0.5 kN/m2 5 Pedestrian Load (TP) 2.5 kN/m2 Source: Data in Research, 2021
3.2.4.Load Due to the Effect of Temperature (EUN)
The calculation of the design temperature is determined as follows:
Minimum average bridge temperature tmin = 15° C Minimum average bridge temperature tmax = 40° C The average construction temperature is taken as follows:
Average bridge temperature = taverage = Temperature expansion, T expansion = 40 – 27.5 = 12.5°C
Shrinkage temperature, T shrink = 27.5 - 40 = -12.5°C
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3.2.5. Wind Loads on Structures (Ews)
Table 3. Calculation of Wind Load in Structure Skew
angle of wind (degre e)
Base wind pressure (Pn)
Lateral Wind Pressure
Longitudinal Wind Pressure Lateral
Load (Mpa)
Longitudi nal Load (Mpa)
Lateral PD (k/N/m2)
Load on Y direction
Longitudi nal PD (kN/m2)
Load on X direction
(kN/m)
0 0.0036 0.0000 2.57 0.90 0.00 0.00
15 0.0034 0.0006 2.42 0.85 0.43 0.15
30 0.0031 0.0013 2.21 0.77 0.93 0.32
45 0.0023 0.0020 1.64 0.57 1.43 0.50
60 0.0011 0.0024 0.78 0.27 1.71 0.60
75 0.0000 0.0000 0.00 0.00 0.00 0.00
90 0.0000 0.0000 0.00 0.00 0.00 0.00
105 0.0000 0.0000 0.00 0.00 0.00 0.00
120 0.0011 0.0024 0.78 0.27 1.71 0.60
135 0.0023 0.0020 1.64 0.57 1.43 0.50
150 0.0031 0.0013 2.21 0.77 0.93 0.32
165 0.0034 0.0006 2.42 0.85 0.43 0.15
180 0.0036 0.0000 2.57 0.90 0.00 0.00
195 0.0034 0.0006 2.42 0.85 0.43 0.15
210 0.0031 0.0013 2.21 0.77 0.93 0.32
225 0.0023 0.0020 1.64 0.57 1.43 0.50
240 0.0011 0.0024 0.78 0.27 1.71 0.60
255 0.0000 0.0000 0.00 0.00 0.00 0.00
270 0.0000 0.0000 0.00 0.00 0.00 0.00
285 0.0000 0.0000 0.00 0.00 0.00 0.00
300 0.0011 0.0024 0.78 0.27 1.71 0.60
315 0.0023 0.0020 1.64 0.57 1.43 0.50
330 0.0031 0.0013 2.21 0.77 0.93 0.32
345 0.0034 0.0006 2.42 0.85 0.43 0.15
3.2.6. Load Combination and Load Factor
Table 4. Load Combination and Load Factor
No Load Combination Type Information
1 STRENGTH I 1.1 MS + 1.4 MA + 1.8 (TD1&2 + TB1&2 + TP1&2) + 1.2 EUN 2 STRENGTH IA 1.1 MS + 1.4 MA + 1.8 (TD1 + TB1 + TP1&2) + 1.2 EUN 3 STRENGTH IB 1.1 MS + 1.4 MA + 1.8 (TD1 + TB1 + TP1) + 1.2 EUN 4 STRENGTH IC 1.1 MS + 1.4 MA + 1.8 (TD1 + TB1 + TP2) + 1.2 EUN 5 STRENGTH ID 1.1 MS + 1.4 MA + 1.8 (TD1&2 + TB1&2) + 1.2 EUN 6 STRENGTH IE 1.1 MS + 1.4 MA + 1.8 (TD1 + TB1 ) + 1.2 EUN 7 STRENGTH IF 1.1 MS + 1.4 MA + 1.8 (TD1&2 + TB1&2 + TP1) + 1.2 EUN 8 STRENGTH II 1.1 MS + 1.4 MA + 1.4 (TT + TD + TB + TP) + 1.2 EUN
9 STRENGTH III 1.1 MS + 1.4 MA + 1.4 EW + 1.2 EUN
10 STRENGTH IV 1.1 MS + 2 MA + 1.2 EUN
11 STRENGTH V 1.1 MS + 1.4 MA + 1.35 (TD + TB + TP) + 1.4 EW + 1.0 EWL + 1.2 EUN 12 SERVICE I 1.0 MS + 1.0 MA + 1.0 (TD1&2 + TB1&2 + TP1&2) + 0.3 EW + 1.0 EWL + 1.2 EUN 13 SERVICE IA 1.0 MS + 1.0 MA + 1.0 (TD1 + TB1 + TP1&2) + 0.3 EW + 1.0 EWL + 1.2 EUN 14 SERVICE IB 1.0 MS + 1.0 MA + 1.0 (TD1 + TB1 + TP1) + 0.3 EW + 1.0 EWL + 1.2 EUN 15 SERVICE IC 1.0 MS + 1.0 MA + 1.0 (TD1 + TB1 + TP2) + 0.3 EW + 1.0 EWL + 1.2 EUN
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16 SERVICE ID 1.0 MS + 1.0 MA + 1.0 (TD1&2 + TB1&2) + 0.3 EW + 1.0 EWL + 1.2 EUN 17 SERVICE IE 1.0 MS + 1.0 MA + 1.0 (TD1 + TB1) + 0.3 EW + 1.0 EWL + 1.2 EUN 18 SERVICE IF 1.0 MS + 1.0 MA + 1.0 (TD1&2 + TB1&2 +TP1) + 0.3 EW + 1.0 EWL + 1.2 EUN 19 SERVICE II 1.0 MS + 1.0 MA + 1.3 (TD + TB + TP) + 1.2 EUN
20 SERVICE III 1.0 MS + 1.0 MA + 0.8 (TD + TB + TP) + 1.2 EUN
21 SERVICE IV 1.0 MS + 1.0 MA + 0.7 EW + 1.2 EUN
Source: Data in Research 2021
3.3 Structural Analysis with SAP2000
After the loads are input to each structural element, a run analysis process can be carried out to generate the internal forces in the structure. The following is the stress ratio of the structural member obtained from the SAP2000 modeling.
Figure 1. Checked structure design
3.3.1. Internal Forcess
Table 5. Internal Forces Recapitulation
Information Pu Vu Mu
Tensile Stress Tensile Stress Positive Negative
Top Chord 2.132 3467.1 3.15 3.15 26.75 22.3
Bottom Chord 606.889 368.87 3.15 3.15 20.25 18.4
Diagonal Bar 2041.64 2072.29 4.27 4.27 20.9 20.6
Source: Data in Research, 2021
3.3.2. Deformation
Deflection analysis on the modeling of the bridge structure is carried out using the SAP2000 application in 3D form using joint supports and rolls at each end. The deflection that occurs is also checked so that it does not exceed the allowable deflection of the bridge which is calculated based on the bridge span, which is L/800.
So for the design of the 40 meter steel frame bridge, the permit deflection in the middle of the bridge span is 50mm.
The value of deformation due to self-dead load is 12.37 mm.
The value of deformation due to live load and dynamic load factor is 22.56 mm.
4. Component Analysis of Truss
In the analysis of a structure, design control is needed to obtain the interaction ratio of axial forces and moments. The interaction ratio is used to measure the safety level of the rod in question. Although the SAP2000 v.20 software includes design control features, sometimes it is better to check manually.
4.1 Compressive Member Control
1. WF Profile 350.350.12.19 2. Pu max = 3467.19 kN43 3. Mu max = 26.75 kN.m
1. Slenderness limitation:
x axis → ≤ 140 = 24,6 ≤ 140 y axis → ≤ 140 = 41,9 ≤ 140 2. Local buckling:
flange → ≤ 0.56 = 9,2 ≤ 13.5 (compact) Web → ≤ 1.49 = 26 ≤ 35.8 (compact) 3. Elastic Flexural buckling:
→ ≤ 4.71 = 55,9 ≤ 113.4 (inelastic buckling) Fe =
=
= 630,02 Mpa Fcr = (0,658
).Fy = (0,658
).345 = 274,33Mpa 4. Nominal Compressive Resistance:
Pn = Fcr . Ag = 274.33 . 17390 = 4770.6 kN Pc = . Pn = 0.85 . 4660.6 = 4293.6 kN
Pr < Pc = 3467.19 < 4293.6 → OK 5. Nominal Flexural Resistance:
Mn = Mp = Zy.Fy 1,6Fy. Sy 776000 345 ≤ 1,6 . 345 . 777000 267,72 kN.m ≤ 428, 9 kN.m
6. Interaction of Acial Compressive and Bending Forces:
if
> 0.2, So:
+ (
≤ 1,0 0.92 ≤ 1,0 → OK
4.2 Tensile Member Control
1. WF Profile 350.350.12.19 2. Pu max = 2042.64 kN 3. Mu max = 20.29 kN.m 1. Gross Section Yielding;𝞍Pn = 𝞍Fy.Ag
𝞍Pn = 0.9 . 345 . 17390
𝞍Pn = 5999,5 kN > 2042,64 kN →OK 2. Net Section Fracture:
𝞍Pn = 𝞍Fu.Ae →where: Ae = An.U
An = Ag – n.d.t →assuming n = 4 bolts & hole diameter = 26 mm = 16142 mm2
Ae = An.U = 16142 . 0,9 = 14527,8 mm2 𝞍Pn= 𝞍Fu.Ae
= 0,75. 490. 14527,8
= 5338,97 kN > 2042,64 kN →OK
3. Check the Slenderness of the Tensile Member;
𝜆f = =
= 75,88 ≤ 200 →OK
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4.3 Steel Truss Connection Detail
Table 6. Planned bolt data
Bold connection type A325 Bolt tensile resistance (Fub) 825 MPa Nominal tensile resistance (Fnt) 620 Mpa Nominal shear resistance (Fnv) 372 Mpa
Bolt Diameter (d) 24 mm
Hole diameter (d') 26 mm Bolt area (Ab) 452.4 mm2 Bolt resistance reduction factor (𝜙) 0.75 Source: Data in research, 2021
4.4 Bolt Resistance
Table 7. Bolt Resistance Recapitulation
Tensile Resistance Shear Resistance Bearing Resistance
212.74 Kn 251.9 kN 402.1 kN
Source: Data in Research, 2021
Due to the type of truss connection getting a shear force, the bolt strength is taken from the shear resistance value of 251.9 kN.
4.5 Number of Bolts Requirements
n =
1. In the horizontal truss with the largest axial force value:
n =
=
n = 14 bolts (one side)
2. In the diagonal truss with the largest axial force value:
n = n = 10 bolts (one side)
4.6 Bolt Distance
1. Bolt spacing
S = 2⅔.d = 2⅔.24 = 64 mm, used → S = 70 mm 2. Minimum edge distance = 1.25.d (minimum)
= 1.25. 24 mm
= 30 mm, used →45 mm
4.7 Gusset Plate Connection Design
The buckling capacity and the compressive stress in the gusset plate may be determined according to Whitmore’s effective width concept. Thus, in design, the gusset plates are treated as rectangular members with a cross section Lw x t, where Lw is the Whitmore’s effective width. In fact, Whitmore defined the effective width as the distance perpendicular to the load, where 30° lines, which are projected from a first bolt row or the end of a weld intersect with a line perpendicular to the member through a bottom bolt row or the second end of the weld.
In this way, it is possible to find the cross section called ―Whitmore Section‖ (Bardot et al., 2017).
Figure 2. reviewed gusset plate location
45 Preliminary gusset plate thickness (tg) = 15 mm Fy = 345 MPa
Fu = 485 MPa
4.7.1. Gusset Plate Design with the Whitmore Method at Members 1, 2, 3 and 4
Figure 3. gusset plate at joint 7
4.7.2. Axial Force Summary of Bolt and Gusset Plate Resistance
Table 8. Recapitulation of bolts and gusset plate resistance End of
Members
Axial load one side gusset(kN)
Shear Strength(kN)
Yield Strength
(kN)
Fracture Condition
(kN)
Block Shear (kN)
Compressive strength/
buckling(kN)
Resistance (kN)
1 1733.6 3526.9 2468.0 2619 1809.4 - 1809.4
2 1036.02 2519.2 - - - 1171.3 1171.3
3 1021.21 2519.2 2423.7 2566.6 1639.2 - 1639.2
4 1733.6 3526.9 2468.0 2619 1809.4 - 1809.4
Souce: Data in Research, 2021
5. Conclusion and Suggestion
Conclusions are obtained from the results of the analysis and interpretation of existing data. While the suggestions are given as reference material in the next research.
5.3. Conclusion
From the results of planning and analysis in the previous chapter, the authors can get the following conclusions:
1. A structural design for the warren truss bridge has been produced which is designed according to the Bina Marga drawing and the loading code of the SNI 1725-2016 bridge, which has a deflection value of less than the maximum allowable deflection required. So that the steel frame bridge has met the requirements and is safe.
2. The maximum steel tension caused by the factored load based on SNI 1725-2016 and AASHTO bridge design specification, overall is still below the allowable tension of each element. So that the dimensions of the planned profile are able to withstand the loads that occur.
3. The number of bolts and gusset plate at the reviewed connection point, is able to withstand the greatest axial force on the truss.
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5.4. Suggestion
The author's suggestions for further research or development based on this research are as follows:
1. It is necessary to compare the superstructure bridge with different types of steel truss so that it can be seen which type of steel truss is more effective in its use.
2. Live load analysis of the vehicle in order to be more detailed, it is better to take into account the running load.
3. More research is needed on the design of the substructure and abutment.
References
Bardot, C., Cábová, K., Kurejková, M., & Wald, F. (2017). Behaviour of a Gusset Plate Connection Under Compression. Stavební Obzor - Civil Engineering Journal, 26(1), 77–90.
https://doi.org/10.14311/cej.2017.01.0008
Purwanto, H., & Hariadi, G. (2018). Analisis Perbandingan Jembatan Tipe Parker dan Tipe Warren dengan Bentang 50 Meter. Jurnal Deformasi, 3, 1. https://doi.org/10.31851/deformasi.v3i1.1963
Sharma, A., & Pahwa, S. (2018). A Review Study on Bridge Truss Structure Analysis. IJSRD-International Journal for Scientific Research & Development|, 6(02), 2321–0613. www.ijsrd.com
