BEHAVIOUR OF STEEL STAGGERED TRUSS SYSTEM UNDER SEISMIC LOADING

Behaviour Of Steel Staggered Truss System Under Seismic Loading, Jijo John K, S. Pradeep, Journal
Impact Factor (2015): 9.1215 (Calculated by GISI) www.jifactor.com
www.iaeme.com/ijciet.asp 177 editor@iaeme.com
1
M.Tech, Structural engineering, Department of Civil Engineering,
Faculty of Engineering and Technology, SRM University, Kattankalathur
2
Asst.Professor (OG), Department of Civil Engineering,
Faculty of Engineering and Technology, SRM University, Kattankalathur
ABSTRACT
Staggered truss system is a prospective steel structure system for multi-story and high-rise
buildings. The staggered truss framing system arose from the use of system design techniques to
improve efficiency in building construction. Staggered truss systems have proved to be effective in
integrating the structural and mechanical requirements. In addition, cost reductions arising from
reduced steel tonnage and reduced building volume may be achieved from the use of these framing
methods. The purpose of this project is analytical investigation on the behavior of an 8-storey steel
staggered-truss system using the ETABS software. The parameters such as the structural truss type,
arrangement of the trusses are varied, and their influences on seismic behaviors of the system are
studied. And based on the test results, some indices of seismic behaviors of the system, such as yield
load, deformation and strength are analyzed.
Index Terms: Steel Staggered Truss, Seismic Loading, Time History Analysis
I. INTRODUCTION
The staggered-truss system (STS) is a new concept in structural steel framing for high-rise
buildings, which was developed in Massachusetts Institute of Technology in 1960s. This system is
efficient for mid rise apartments, hotels, motels, dormitories, hospitals, and other structures for which
a low floor to-floor height is desirable. As shown in Figure 1.1, the system consists of a series of
storey-high trusses spanning the total width between two rows of exterior columns and arranged in a
staggered pattern on adjacent column lines. With the columns only on the exterior walls of the
building, the usual interior columns are omitted, thus providing a full width of column-free area. [1]
BEHAVIOUR OF STEEL STAGGERED TRUSS SYSTEM
UNDER SEISMIC LOADING
Jijo John K1
, S. Pradeep2
Volume 6, Issue 6, June (2015), pp. 177-186
Article Id: 20320150606018
International Journal of Civil Engineering and Technology (IJCIET)
© IAEME: www.iaeme.com/Ijciet.asp
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
IJCIET
© I A E M E

Fig. 1.2. (a) Hybrid truss and (b) open-web truss
The staggered arrangement of the storey-high trusses placed at alternate levels on adjacent
column lines allows an interior floor space of twice the column spacing to be available for freedom of
floor arrangements. To resist gravity loads, the floor system may be considered to be a series of
simple spans or continuous for two column spacing. As a continuous system, the floor members rest
on the top chord of one truss and extend to the bottom chords of the two adjacent trusses.
The floor reactions to the gravity loads become the applied loads on the top and bottom
chords of the trusses. The general requirements for the storey-high trusses are to span the total
transverse dimension of the building, support the gravity loads directly, and provide the necessary
resistance to the lateral loads. The truss must provide an opening near the center of span to permit a
width and height of sufficient proportions to be used as a corridor. The Pratt truss (also called as
hybrid truss, as shown in Figure 1.2(a)) with diagonals omitted for passage ways is the most efficient
type of truss to be used in the staggered-truss system [2]
Fig. 1.2. (a) Hybrid truss and (b) open-web truss.
The Vierendeel truss also called as open-web truss, as shown in Figure 1.2(b), by the nature
of its design with open panels, is another efficient truss to be used in this system.
With large lateral stiffness and little lateral displacement, Fig. 1.1 Staggered-truss system
staggered-truss system is one reasonable and efficient lateral force resisting system. Its
capability of deformation is similar to that of frame-shear wall structure and lies between those of
frame structure and shear wall structure. The floor system is acting as a deep beam and must be
designed to resist the in-plane shears and the resulting in-plane bending moments.
The shear forces caused by horizontal loads is transferred to the upper chords of the trusses by
the floor slabs and the connections between the floor slabs and the chords, then to the lower chords
by inclined members of trusses, and to the foundation gradually in the end, as shown in Figure 1.3.
The combination of co1umns, longitudinal linking beams and braces can bear the longitudinal
horizontal loads effectively. The researches of MIT also showed that the steel consumption of the
staggered-truss system was less than that of the steel frame by 50%, and less than that of the braced
steel frame by 40%, for multi-storey or high-rise hotels and resident buildings. By virtue of its
excellent lateral stiffness and reasonable cost, steel staggered-truss system was already used in a few
hotel, apartment, office and hospital buildings in America and Canada.

Fig.1.3. Delivering route of lateral load within the STS
Previous researches on steel staggered-truss system concentrated on the theoretical analyses,
and the experimental studies on the seismic behaviors of it have never been reported. So in this
project an analytical investigation on seismic behaviors of an 8-storey steel staggered-truss system is
carried out. It is done using ETABS software. Both the material and geometric nonlinearity are
considered in the method. The parameters, such as the structural truss type, arrangement of the
trusses are varied, and their influences on seismic behaviors of the system are studied.
II. MATERIAL DESCRIPTION
A staggered-truss frame is designed with steel framing members and concrete floors. Most
often, the floor system is precast concrete slab. The trusses are manufactured from various steels.
Early buildings were designed with chords made of wide-flange sections and diagonal and vertical
members made of channels. The channels were placed toe-to-toe, welded with separator plates.
The properties of structural steel result from both its chemical composition and its method of
manufacture, including processing during fabrication. Standard properties of steel are given in Table
2.1. Product standards define the limits for composition, quality and performance and these limits are
used or presumed by structural designers.
Table 2.1standard Properties of Steel
Sl. no: Property Value
1 Yield strength 250 N/mm2
2 Density 7850 Kg/m3
3 Young’s Modulus 2.1x105
N/mm2
4 Shear Modulus 80000N/mm2
5 Poisson’s Ratio 0.3
III. MODELING
The innovative and revolutionary new ETABS is the ultimate integrated software package for
the structural analysis and design of buildings. The latest ETABS offers unmatched 3D object based
modeling and visualization tools, blazingly fast linear and nonlinear analytical power, sophisticated
and comprehensive design capabilities for a wide-range of materials, and insightful graphic displays,
reports, and schematic drawings that allow users to quickly and easily decipher and understand

analysis and design results. From the start of design conception through the production of schematic
drawings, ETABS integrates every aspect of the engineering design process. Creation of models has
never been easier - intuitive drawing commands allow for the rapid generation of floor and elevation
framing.
A. Analytical Model
The structure has been stimulated in three dimensional steel staggered truss systems with
similar spans and varying type of trusses. The columns are fixed at the base. Eight full-scale FE
models with plan dimensions of 24X16.8m are constructed for parametric analyses. All the models
are composed of five parallel frames with spacing of 6m and each planar frame consists of storey-
high trusses with span of 16.8m, arranged alternately in vertical direction. But the truss type and
arrangement of the ground floor trusses are different with each other.
The steel sections which are used for the framing of staggered truss system are wide parallel
flange beams (WPB). The model of typical I section is shown in Figure 3.1. These are doubly
symmetric shapes, generally used as beams or columns [3]. Beams or columns under the standard
have nominal flange width same as depth up to nominal beam depth 300 mm. The sectional
properties of steel sections are given in below in Table 3.1. Beam depth larger than 300 mm have
nominal flange width 300 to 400 mm. Columns have flange two numbers of hybrid trusses at each of
the second, fourth and sixth floors, and two each at the third and fifth floors. The arrangement of
trusses at top floor is same as that of the first floor. The truss properties are mentioned in Table 3.2
widths more than the depths. Beams and column section are manufactured with heavy, medium and
light flange and web thickness. Beams and columns are designated by nominal depth and nominal
flange width and mass in kg/m.
Table 3.1: Sectional Properties of Steel Sections
Mass Depth Width Web Flange
Sl No: Designations
(kg/m) (D)mm (B)mm (t)mm (T)mm
Column
1 WPB 191.10 368 391 15.0 24.2
400X400
Beam
2 ISMB 103.7 600 210 12 20.8
600
3
Chords
99.5 600 210 10.5 15.5
ISLB 600
Fig. 3.1 Parallel flange section

B. MODEL 1: Structure with three hybrid trusses at first floor.
In this type of structure the first floor consists of hybrid trusses at first, third and fifth frames
and open-web trusses at the second and fourth frames as shown in Figure3.2. There are
Fig. 3.2 Model 1
Table 3.2: Properties of Model 1
Sl no: Name Model 1
1 Dimension 24X16.8 m
2 Type of truss Hybrid truss
3 Number of storeys 8 m
4 Height of each storey 3 m
5 Column WPB 400X400
6 Beam ISMB 600
7 Chords ISLB 600
8 Type of floor Concrete
9 Thickness of floor 0.10 m
C. MODEL 2; Structure with three open trusses at first floor
In this type of structure the first, third, fifth and seventh floors consist of open-web trusses at
first, third and fifth frames as shown in Figure 3.3. Also there are two numbers of open-web trusses at
each of the second, fourth and sixth floors. The properties of truss are mentioned in Table 3.3
Sl no: Name Model 2
2 Type of truss Open-web truss
6 Beam ISMB 600
7 Chords ISLB 600

D. MODEL 3: Normal framed structure.
This structure is modeled with normal frame as shown in Figure 3.4. There are four and five
columns in x and y directions respectively. The columns in x direction are placed with a spacing of
5.6m each. The truss properties are mentioned in Table 3.4
Fig. 3.4 Model 3
Sl no: Name Model 3
2 Type of truss Normal frame
6 Beam ISWB 600
IV. ANALYSIS
A. Loading Scheme
The Time History Response of a structure is simply the response (motion or force) of the
structure evaluated as a function of time including inertial effects. The time history analysis in
ETABS allows base displacements as loading type. Again, the Base Acceleration loading type uses a
text file for input. The base acceleration is very similar to the base displacement and represents
putting the structure through some varying ground acceleration over time. Logically, the base
acceleration is just the second derivatives of the base displacements. Similarly, the accelerations can
act in the x, y, and z directions and again they can be any combination of all or some of these
directions. To perform a time history analysis you must first create a new time history case.
Use the Time History Function Definition - From File form to add or modify a time history
function definition from a text file.
• Time History Function Name edit box. Use the default or specify another name for the time
history function by typing directly in the edit box.
• Function File area and File Name display box. Click the Browse button to access the Pick
Function Data File form and specify the location and filename of the time history data text file.
Click the View File button to open the text file in the default text editor to make any necessary
adjustment to the text file to accommodate how the program reads the text file:

B. El Centro Loading
The 1940 El Centro earthquake (or 1940 Imperial Valley earthquake) occurred at 21:35
Pacific Standard Time on May 18 in the Imperial Valley in south eastern SouthernCalifornia near the
international border of the United States and Mexico. It had a moment magnitude of 6.9 and a
maximum perceived intensity of X (Intense) on the Mercalli intensity scale. The earthquake was
characterized as a typical moderate-sized destructive. It was the strongest recorded earthquake to hit
the Imperial Valley, and caused widespread damage to irrigation systems and led to the deaths of
nine people.
A strong-motion seismograph at El Centro recorded the earthquake and provided the first
example of such a recording made very close to a fault rupture in a major earthquake. The graphical
representation of El Centro loading is show in Figure. 4.1. This gave a detailed record of the different
types of shaking associated with the earthquake. It is often used in design of earthquake-proof
structures today, particularly for the time history analysis method. The recording showed that the
earthquake consisted of several sub-events, with a total of 13 being recorded in just over five
minutes. The majority of the energy released during the earthquake occurred in the first fifteen
seconds, although significant energy was released as late as the last of those events, near the 5:20
mark on the seismograph record.
Fig. 4.1
V. RESULTS AND DISCUSSION
In this study two models of eight storey steel staggered truss system and one model of normal
frame has been designed and their seismic performances has evaluated by time history analysis.
A. Storey Displacement
Fig. 5.1 Storey displacement in X direction

Fig. 5.1 Storey displacement in Y direction
TABLE 5.1
STOREY DISPLACEMENT IN X DIRECTION
Storey
Model 1 (mm) Model 2 (mm)
Model 3
no: (mm)
1 3.6 12.1 28.8
2 5.7 53.3 69.3
3 7.6 108.3 108.1
4 8.8 160.5 143.6
5 10.4 201.5 171.5
6 11.3 258.9 197.1
7 12.4 355.7 216.1
8 12.9 464.7 227.8
According to the analytical results the staggered truss system with hybrid truss and open web
truss showed superior seismic load resisting capacity in the longitudinal direction of the building than
the normal frame. The storey displacements of three models in both X and Y directions are shown
below in the Table 5.1 and Table 5.2.
In the case of longitudinal direction the model with hybrid truss showed the maximum
seismic load resisting capacity with least storey displacement. The storey displacement in X and Y
directions are shown in Figure 5.1 and Figure 5.2 respectively.
Table 5.2: Storey Displacement in Y Direction
Storey
Model 1 (mm) Model 2 (mm) Model3 (mm)
no:
1 14.1 13.8 24.2
2 34 33.3 52.8
3 52.7 51.6 76.1
4 69.1 67.5 94.5
5 82.4 80.4 112.5
6 92.5 90.3 130.6
7 99.4 97.1 143.6
8 103.1 100.9 156.8

B. Storey Shear
The storey shear in the models shows an increasing manner in the values according to the
height of building. The storey shear in X direction for model 2 have the least value and the model
with normal frame have the highest value of storey shear. The graphical representation of storey
shears of three models in X and Y direction are shown in Figure 5.3 and Figure 5.4 respectively. At
the same time the value of storey shear in Y direction for models framed with hybrid trusses and
open web truss shows almost the same value. While comparing the three models it could be
concluded that the normal framed structure has the highest value of storey shear.
Fig. 5.3 Storey shear in X direction
Fig. 5.3 Storey shear in Y direction
VI. CONCLUSION
The seismic analysis of steel staggered truss system has been completed and from the results
it is clear that among the three structures modeled, the structure with hybrid truss have maximum
strength. This structure has the minimum value of lateral displacement in both X and Y directions.
The maximum value of lateral displacement and maximum value of storey shear is observed
for the structure with normal frame. The storey shear in Y direction for Model 1 and Model 2 have
almost the same value. The storey shear of the structure with normal frame has been observed as
decreasing as the height of the building increases.
REFERENCES
1. Jinkoo Kim, Joon-Ho Lee, Young-Moon Kim, (2007) “Inelastic behavior of staggered truss
systems”, Wiley Interscience, Structural design of tall and special buildings 16: pp 85–105
2. XuhongZhou, YongjunHe, LeiXu, QishiZhou, (2009) “Experimental study and numerical
analyses on seismic behaviors of staggered-truss system under low cyclic loading”, Elsevier
Ltd Thin-Walled Structures 47: pp 1343–1353

3. IS 12778 (2004): Hot Rolled Parallel Flange Steel Sections for Beams, Columns and Bearing
Piles - Dimensions and Section Properties.
4. IS 1893 (part 1): (2002) “Criteria for earthquake resisting design of structures,”
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system”, Advances in Steel Structures, Vol. II 1323 Z.Y. Shen et al. (Eds.) Elsevier Ltd: pp
1323-1328
6. Chang-kun Chen, WeiZhang, (2011) “Experimental study of the mechanical behavior of steel
staggered truss system under pool fire conditions”, Thin-Walled Structures 49: pp 1442–1451
7. K.K.sangle, K.M.bajoria, V.Mhalungkar, (2012) “Seismic analysis of high rise steel frame
building with and without bracing”, 15 WCEE Lisboa: pp 1-10
8. David Stringer, (1982) “Staggered truss and stub girder framing systems in western Canada”,
Canadian structural engineering conference: pp 3-8
9. Scalzi JB, (1971) “The staggered truss system-structural consideration”. Engineering Journal
AISC; 8 (10): pp 25–30.
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11. N. Umamaheswari and Dhanya Mary Alexander, “A State of The Art Report on Fatigue
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BEHAVIOUR OF STEEL STAGGERED TRUSS SYSTEM UNDER SEISMIC LOADING

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