Modular Steel Girder Design for 40 m, 50 m and 60 m of Span in
Indonesia
By
Sudahraa), Febry Pernatab)
Synopsis
Indonesia is an archipelagic country with large population. There is about 17,500 of islands and
261 million of population. Even though Indonesia is a large country, the population is concentrated
in few regions. Geographical conditions and patterns of population distribution require the
development of appropriate infrastructure such as bridges to connect between islands and elevated
highway or flyovers to overcome land constrains. Currently steel structure is more popularly used
for girder on bridge and elevated highway. Some of advantages on steel compared to concrete base
are faster in fabrication and assembling, high quality cost but optimally distributed for the large
number of spans, as well as better term for aesthetic.
This paper describes in brief the experiences of PT Krakatau Steel (PTKS) in designing of modular
steel girder for 40 m, 50 m and 60 m of span. PTKS is assisted by PT. LAPI ITB as a independent
consultant in term to get prime and appropriate design for the girder. The design purposely
considers the local steel optimization. The steel girder dimensions and properties are designed to
utilize steel plate from PTKS and Local Steel Companies with 450 – 550 Mpa of yield strength,
20 – 24% of elongation, 1,700 – 2,500 mm of width and 20 – 22 mm of thickness. The design
method and calculations are based on regulations and standard that apply in Indonesia. Analysis
and calculation focused on the steel girder while pier, pierhead and foundation will adjust to the
topography, soil type and seismic parameters of the location. Additionally, the production cost
becomes lower so that be overall cost of the girder or even the project becomes more competitive.
The PTKS steel girder design expected to be default design for development of bridges and
elevated highway or flyovers in Indonesia. So that the constructions are faster, high quality, low
budget and better aesthetic. Besides, the role of local steel companies will be more optimal.
Keywords: Modular Steel Girder, 450 – 550 Mpa of yield strength, 1,700 – 2,500 mm of width
a) Engineer of Technology Development, PT Krakatau Steel (Persero) Tbk b) Senior Engineer of Mechanical & Civil Engineering, PT Krakatau Steel (Persero) Tbk
I. INTRODUCTION
Infrastructure development play important role to accelerate economic growth. Indonesia
is an archipelagic country with large population. However, the population is concentrated in few
regions. Geographical conditions and patterns of population distribution of Indonesia require the
development of appropriate infrastructure such as bridges to connect between islands and elevated
highway or flyovers to overcome land constrains. PT Krakatau Steel has responsibility to support
the development of the infrastructure in accordance with its competence as steel provider.
Currently in infrastructure development, steel structure is popular and play important role
to achieve efficient structure by time and cost. For bridges and elevated highway, the girder can
replaced by steel structure for concrete structure. Some of the reasons are faster in fabrication and
assembling, high quality cost but optimally distributed for the large number of spans, as well as
better term for aesthetic. But for reason of local steel optimization, the design of steel girder should
be meet with capability of local steel companies.
In order to get appropriate girder design which can overcome static and dynamic loads
according to Indonesia base condition and also to accommodate local steel, there two parameters
can be adjusted. They are the dimension of the steel girder and properties of the steel.
II. STEEL GIRDER
Girder is part of upper structure on bridge or elevated highway that serves to channel loads
such as vehicle load, the weight of the girder itself and the other loads above the girder to the lower
part of the structure. Generally, the girder can be in form of profile beam I (I-Girder), Box (Box
Girder) and other shapes that designed as needed. There are five form of girder that are widely
used today, they are I-Girder, Box Girder, U-Girder, T-Girder and Plate Girder.
(a) I-Girder (b) Box Girder (c) U-Girder
(d) T-Girder (e) Plate Girder
Figure 1: Shapes of Girder
All forms of girder can be made of steel or concrete. But for short span it is not
recommended to use steel girders because of the initial high cost.
Currently, the use of steel structures for girders has been very popular. Demands to
produce strong structures at lower costs and faster have led to many innovations related to
construction such as steel girder. There are several advantages of steel girder when compared to
concrete girders such as table 1.
Table 1. Advantages of Steel Girder
Point of
comparation Steel Girder
Concrete
Girder Effect Benefit
Strength to
weight ratio
High Low - good resist of
static load
- longer span
- easier to handling
- low requirement of
foundation
Low cost in total
material,
transportation
and handling.
Formability High Low - faster in
construction
- easier to joint
- more aesthetic
Saving in time
for construction
and assembling
Scrap value Yes No can be recycled Green structure
Ductility High Low - no sudden failure
- can withstand
earthquake more
effectively
- more safe
III. PLAT STEEL PROVIDER IN INDONESIA
Indonesia is one of the largest steel producing countries in Southeast Asia. based on data from
SEAISI in 2018, in 2017 Indonesia was ranked as the 2nd ranked producer of steel in Southeast
Asia with steel production growth of 19.5%. While the first rank of steel producer in Southeast
Asia is Vietnam, which recorded substantial steel production growth 30.5%. Here are the 6 major
steel producing countries in Southeast Asia.
Table 2. Six largest Southeast Asian steel producing countries
Country 2016
Production (tons)
2017
Production (tons)
2017
Portion (%)
Growth
y-o-y (%)
Indonesia 6.582.234 7.866.362 22,7% 19.5%
Malaysia 3.781.668 3.772.057 10,9% -0,3%
Philippines 4.346.038 4.300.249 12,4% -1,1%
Singapore 528.453 595.522 1,7% 12,7%
Thailand 7.977.590 6.875.446 19,8% -13,8%
Vietnam 8.657.000 11.302.000 32,6% 30,6%
ASEAN – 6 Total 31.872.983 34.711.636 100% 8,9%
Development & infrastructure projects that are in line with the policies of the Government of
Indonesia play an important role in the growth of the steel industry in Indonesia for the last 3-5
years. This is evidenced by the increasing budget for infrastructure projects as shown in the
following figure.
Figure 1. Indonesia Infrastructure Budget
In Indonesia there are several steel companies that produce plates as raw material for steel girder,
here are some companies that produce steel plates:
Table 3. Indonesia Steel Plate Provider
Company Work/Location Product
Thickness (mm)
Product
Width (mm)
PT Krakatau Steel Cilegon, West Java 1,2 - 25 600 - 2250
PT Krakatau Posco Cilegon, West Java 6,0 - 120 1200 - 4650
PT Gunung Bekasi, West Java 5,0 – 150 1200 - 3550
PT Jayapari Steel Surabaya, East Java 8,0 – 25 900 – 1550
PT Gunawan Surabaya, East Java 6,0 – 80 1200 - 2500
IV. STEEL GIRDER DESIGN FOR 40 M, 50 M AND 60 M
The design method and calculations are based on regulations and standard that apply in Indonesia.
Analysis and calculation focused on the steel girder while pier, pierhead and foundation will adjust
to the topography, soil type and seismic parameters of the location.
4.1 Structure System
Top structure system of modular bridge or high way is simple span of steel girder structure with
the following information:
a. Girder profile : Composite U Girder
b. Span (L) : 40, 50 and 60 meters
c. Height of girder : 1.7 m (L=40 m) ; 2 m (L=50 m) ; 2.5 m (L=60 m)
d. Width of Girder : 2,0 meters
0%
5%
10%
15%
20%
0
100
200
300
400
500
2013 2014 2015 2016 2017
TrilionRupiah
Infrastructure Budget % of total Budget
e. Number of girder : 3 Girder
f. Number of lines : 3 lines * 3.5 meters
g. Design for vehicle : Truck 50 tons
Figure 2. Dimension of Modular bridge Cross Section in mm
4.2 Standard and Code References
This bridge structure system will be analyzed based on several standards and codes that apply in
Indonesia and other standards are as follows:
a. SNI 1725 – 2016 : Peraturan Pembebanan untuk Jembatan
b. RSNI T03 – 2005 : Peraturan Baja untuk Jembatan
c. RSNI 03 – 2833 – 201x : Perancanagan Jembatan terhadap Beban Gempa
d. AISC Steel Design LRFD
e. AAHTO LRFD Bridge Design Specifications 6th Ed-2012
4.3 Specification of Steel Material
Specification of material that used for the girder and accessories as follows:
a. Steel for U Girder
Grade : JIS G 3106 SM570
Yield Strength : 450 – 540 Mpa
Young Modulus : 200,000 Mpa
Coef. Expansion : 1.20e – 0.5 per Celsius degree
Poisson Ratio : 0.3
Specific Weight : 7850 kg/m3
Elongation : 20 – 24%
b. Steel for Diaphragm and Stiffener
Grade : JIS G 3106 SM520 B
Yield Strength : 355 – 520 Mpa
Young Modulus : 200,000 Mpa
Coef. Expansion : 1.20e – 0.5 per Celsius degree
Poisson Ratio : 0.3
Specific Weight : 7850 kg/m3
4.4 Type of Load
In general, the loading criteria that used in design is consider and reviewed by condition as follows:
Working load/Service load
Working load/service load is load that works during bridge service conditions, this is
related with bridge serviceability.
Ultimate load
Ultimate load is load that obtained from multiply the work load by load factor.
Plan load in this design are categorized to be 2 categories namely permanent load and transient
load. The following is categorization for loads that applied for this design:
1. Permanent Load:
Symbol Description
MS Load of structural and nonstructural bridge component
MA Pavement and utility dead load
TA Horizontal lateral load of soil
PL Forces on bridge structure that occurred by implementation process
PR prestress
2. Transient Load:
Symbol Description Symbol Description
SH Force due to shrinkage TP Pedestrian load
TB Force due to brakes SE Load due to decline
TR Centrifugal force ET Force due to temperature gradient
TC Force due to vehicle collisions EUn Force due to uniformity of temperature
TV Force due to ship collisions EF Buoyant force
EQ Earthquake force EWs Wind load on the structure
BF Friction force EWl Wind load on the vehicle
TD Lane load “D” EU Stream and drift load
TT Truck load “T”
A combination of SNI 1725 2016 factored loading for service life and ultimate conditions are as
table 4.
Table 4. Load combination of SNI 1725 2016
4.5 Bridge Structure Modeling and Analysis
a. Bridge Structure Modeling
Modeling and analysis for main bridge are simulated by MIDAS Civil. Bridge modeling
presented as overall of top bridge structure that consist of girder, pierhead, and pier. All
component modeled as beam element/frame but girder modeled as special beam element
which have composite section. Placement of box girder on pierhead is modeled as boundary
condition rigid link which one end of rigid link is set as hinge and the other one is set as
roller so can represent simple span on girder.
Figure 3. Modeling of Bridge Structure
b. Girder Shape
The steel girder is designed as U-Type girder as shown as follows:
Figure 5. Shape of Steel Girder
c. Bridge Structure Analysis
After modeling the bridge structure and input the loads, the next step is to analyze the
structure by calculations and computer program (MIDAS Civil) to get structure response
in the form of internal force such as axial, shear, and moment of force. The following are
the simulation result with the MIDAS Civil for span 60 m:
Post Construction Stage:
Figure 6. Diagram of moment, summation final stage
Condition due to a combination of strength loads enveloped (kuat I, II, III, IV, V):
Figure 7. Diagram of Moment My, Enveloped strength combination
Figure 8. Diagram of Moment Mz, Enveloped strength combination
Condition due to a combination of extreme loads envelope (extreme I, II):
Figure 9. Diagram of Moment My, Extreme envelope combination
Figure 10. Diagram of moment Mz, extreme envelope combination
V. CONCLUSION OF DESIGN
Modular bridge calculations and analyze have been carried out in accordance with applicable
structural design and loading rules. The following are conclusion of steel U girder design for
composite bridge modular:
Steel grade is SM 570 or 450 – 550 Mpa of yield strength, 20 – 24% of elongation with dimension
of girder:
1. Steel U Girder for modular bridge 40 m of span
2. Steel U Girder for modular bridge 50 m of span
3. Steel U Girder for modular bridge 60 m of span
Reference
1. LAPI ITB & Krakatau Steel, Desain Struktur Jembatan Modular Span 40, 50 dan 60
m,Dok. Krakatau Steel, Indonesia 2017
2. Faqih Ma’arif, M.Eng., Analisis Struktur Jembatan, Learning Module, University of
Negeri Yogyakarta, Indonesia, 2012.
3. Civildigital.com, Complete Comparison of Steel and Concrete, 2018.
4. Badan Standardisasi Nasional, Pembebanan untuk Jembatan, SNI 1725:2016, Indonesia,
2016.