Staggered Truss Framing Systems solution for high-rise building

Abstract

Steel frames often have large deformations under the actions of lateral loads, especially in high-rise buildings. To avoid this problem, the steel frame is combined with reinforce concrete walls or truss systems. Although used popular, reinforce concrete walls still reveal some disadvantages. Therefore, this paper investigates the behaviour of the staggered truss framing systems for high-rise buildings. Based on the investigated results, recommendations are given for the efficiency of the structural solutions.

Full text

ISBN: 1
The 11th National Conference on Solid Mechanics
Ho Chi Minh city, 7-9 Nov 2013
Staggered Truss Framing Systems solution for high-rise building
Quoc Anh Vu, Ngoc Hieu Pham
Faculty of Civil Engineering – Hanoi Architectural University
E-mail: vquocanh@gmail.com
Abstract: Affected by lateral loads, steel frames often have large deformation, especially steel
frames in high-rise buildings. To avoid this problem, steel frame is combined with reinforce
concrete walls or truss systems. Although used popular, reinforce concrete walls still reveal some
disadvantages. Consequence, this paper represents staggered truss framing systems for high-rise
buildings. According to surveys and calculation this structure, this paper gives some comments and
the efficiency of this solution.
Key words: staggered truss framing systems, high-rise building.
1. Introduction
Steel is one type of construction materials that has highest level in bearing capacity. In
addition, it also has advantages in both time and cost saving in manufacturing and
constructing activities. As the result, in the future steel structure is proposed for further
development in high-rise building aspects.
Characteristic of high-rise building frame requires to have a guarantee for bearing capacity
and meet requirement for deformation standard such as displacement of top-housing
position or a stabilizing in general structure. It is difficult to satisfy all mentioned
requirement if only steel frame is used. Therefore, to guarantee for rigidity standard, the
construction can apply one or both reinforce concrete walls and truss systems.
Although reinforced concrete walls commonly use in high-rise building ,it also revealed
some limitations such as the inflexibility of space, too much concentration on lateral load
of the walls and low level in utilizing bearing capacity of steel columns and beams.
Therefore,steel truss systems can be applied as supported system, along with reinforce
concrete walls to reduce the limitation and enhance the advantages for each systems to
improve productivity.

2 Vũ Quốc Anh, Phạm Ngọc Hiếu
Applying truss systems in high-rise buildings in Vietnam still has many limitations.
Therefore it should be studied and applied more widely. Here's works at 169 Nguyen Ngoc
Vu that applied truss system in structural solutions.
Hình 1. Staggered Truss Framing Systems
2. Characteristic of reinforce concrete wall and truss system which bearing lateral load
a. Reinforce concrete walls
Reinforce concrete wall can enhance lateral rigidity level of the construction. Deformation of
top housing position will be equal to total deformation of its components. This deformation is
presented by diagram as figure 2. The reasons that cause deformation are Shear deformation, axis of
frame system create the highest level of angle. whereas, cause of deformation in core of reinforced
concrete is majority caused by bending, leading to the maximum angle at the top of the building.
When being affected by lateral load, the frame and core of reinforced concrete walls interacts
with each other and creates deformation shaped S as the below figure. This interaction makes the
frame to be affected by lateral load in the top position and the core to be affected at the bottom of
the building.

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Hình 2. The combination of reforce concrete frames and reforce concrete walls
b. Staggered truss
The role of web members in resisting the horizontal shear can be demonstrated by following the
load path down the braced bent. Consider the braced frames, shown in Figure 3, subjected to an
external shear force at the top. In Figure 3a, the diagonal in each story is in compression, causing
the beams to be in axial tension; therefore, the shortening of the diagonal and extension of the
beams gives rise to the shear deformation of the bent. In Figure 3b, the forces in the braces
connecting to each beam-end are in equilibrium horizontally with the beam carrying insignificant
axial load. In Figure 3c, half of each beam is in compression while the other half is in tension. In
Figure 3d, the braces are alternately in compression and tension while the beams remain basically
unstressed. And finally in Figure 3e, the end parts of the beam are in compression and tension with
the entire beam subjected to bending in double curvature as shown by the dotted lines. Observe that
with a reversal in the direction of horizontal load, all actions and deformations in each member will
also be reversed. [4]
Figure 3. The load path down of braced frame.

4 Vũ Quốc Anh, Phạm Ngọc Hiếu
c. Staggered Truss Framing Systems
Staggered Truss Framing Systeems has been used commonly in the world and be shown as
figure 4. A system commonly referred to as staggered truss system evolved as an outgrowth of the
study. In this system story-high trusses span the entire width of the building in the transverse
direction between exterior columns. The trusses are arranged in a staggered pattern at alternate
floors, as shown schematically in Figure 4. The floor acts as a diaphragm transferring the lateral
loads to the trusses. The columns, therefore, receive no bending moments by frame action. To allow
for an uninterrupted corridor, the truss diagonals are eliminated at the location of corridors,
typically at the center of the truss. Since the diagonals are eliminated, the shear is carried by
Vierendeel action of the truss vertical members and the top and bottom chords. [4]
Figure 4. Staggered Truss Framing Systems
The columns in-between the floors, as shown in Figure 5, receive no bending moments due to frame
action. It is as though the entire building has a vertical truss for the entire height, resulting in an
efficient structure. Since the trusses are placed at alternate levels on adjacent column lines, twobay-
wide column-free interior floor space is created in the longitudinal direction.

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Hình 5. Conceptual two-dimensional model for staggered truss system [4]
The building at 169 Nguyen Ngoc Vu street become the first project in Vietnam that is applied
Staggered Truss Framing Systems. The reinforced concrete walls system is constructed by Sliding
formwork and Staggered Truss Framing Systems and the Staggered Truss Framing Systems is
implemented by Erection method. As proven through calculation based on theory as long as
practical construction, Staggered Truss Framing Systems has some advantages:
- Reduce the load for the foundation thanks to load reduction by its self
- Reduce time to implement the project thanks to Sliding formwork application for reinforce
concrete and erection method for the frame system. As the statistics in USA and Canada,
the time to complete construction will reduce by 20% to 25% compared with in site
concrete.
- Applying Staggered Truss Framing Systems that is combined by hệdàncáchtầngvàcáchnhịp
can not only reduce the cost compare with Continuous Framing systems but also enhance
flexibility for the space of the building as well as advantage in bearing capacity of Truss
Framing.
3. Example
The model is based on the building in 169 Nguyen Ngoc Vu Street – Thanh Xuan District –
Hanoi. This building is used for researching and office works including 21 floors with typical high
for each store is 3 metters and its structure plan is shown in figure 6.
Structure solution is the combination of reinforce concrete walls and steel frame systems
(columns, beams and braces). The steel frame systems are not connected directly with reinforce

6 Vũ Quốc Anh, Phạm Ngọc Hiếu
concrete walls, but through floors. As a result, two above systems work together to resistant lateral
loads.
Materials:
- Concrete B35; Plate steel: f = 360
2
(N/mm )
- Bar steel:
+ D<10, steel CI, Ra= 225
2
(N/mm )
+ 10  D <20, steel CII, Ra=280
2
(N/mm )
+ D ≥ 20, steel CIII, Ra= 365
2
(N/mm )
The building is calculated with 3 structural solutions:
Solution 1: The combination of reinforce concrete walls and steel frames (columns & beams)
Solution 2: The combination of reinforce concrete walls and Staggered Truss Framing
Systeems 1.
Solution 3: The combination of reinforce concrete walls and Staggered Truss Framing
Systeems 2.
.The model is calculated by software Etabs 9.7.2.0 and the results are:
Table 1. The cross-sections for columns, beams & braces
Components
Solution 1
Solution 2
Solution 3
Floor 1-10
Floor 11-21
Floor 1-10
Floor 11-21
Floor 1-10
Floor 11-21
Column
H800
H600
H300
H200
H300
H200
Beam
I(600x200)& IPE 360
H160 & IPE360
H160 & IPE360
Brace
-
H120
H120
Figure 6. Structure plan

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Figure 7. Staggered Truss Framing Systeems 1 (Solution 2)
Figure 8. Staggered Truss Framing Systeems 2 (Solution 3)
a) Solution 1 b) Solution 2 c) Solution 3
Hình 9. The models of building
Loads:
+ Death loads are calculated by the software 9.7.0.0.
+ Live loads: khu hành lang lấy 360(daN/m2), khu làm việc lấy 240 (daN/m2), có xét thêm hệ số
giảm hoạt tải của nhà nhiều tầng.
+ Wind load: Hanoi, wind area IIB.
+ Earthquake Load.
Combination of loads:

8 Vũ Quốc Anh, Phạm Ngọc Hiếu
Combination 1: Dead load + Live load
Combination 2: Dead load + Wind load
Combination 3: Dead load + (Wind load + Live load)*0.9
Combination 4: Dead load + Live load *0.8 + Wind load *0.5 + Earthquake load.
The limitation of deformation at the top of building is 10 centimeters; the deflection of beam is 3
centimeters.
Based on Ultimate limit state and Serviceablility limit state, the results are:
Table 2. The frequency of the building (Unit: second)
Axis
frequency
Solution
Solution
Solution
I
II
III
Axis
f1
1.630
1.677
1.641
X
f2
0.416
0.381
0.378
f3
0.337
0.192
0.191
Axis
f1
2.233
1.838
1.837
Y
f2
0.479
0.430
0.430
f3
0.198
0.187
0.187
Axis
f1
0.892
0.892
0.890
Z
f2
0.236
0.290
0.289
f3
0.167
0.148
0.148
Table 3. The deformation of building in axis Y (unit: cm)
Story
Solution I
Solution II
Solution III
Top
10.41
7.24
7.26
15
7.57
4.95
4.96
10
4.31
2.92
2.92
5
1.47
1.06
1.06
Table 4. The deformation of building in axis X (unit: cm)
Story
Solution I
Solution II
Solution III
Top
4.70
5.28
5.04
15
3.21
3.57
3.43
10
1.88
2.08
2.01
5
0.69
0.74
0.73

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Table 5. Forces in walls (unit: kN-m)
Story
Solution I
Solution II
Solution III
Mx
897
1237
1262
Roof
Vx
242
358
390
My
691
422
419
Vy
224
145
145
Mx
6052
7249
7036
15
Vx
616
611
605
My
7875
6027
6044
Vy
687
438
438
Mx
11376
13091
12673
10
Vx
889
824
823
My
11171
8451
8453
Vy
805
471
472
Mx
20803
22347
21880
5
Vx
1336
1322
1322
My
16019
11891
11875
Vy
1368
955
956
Table 6. Forces in Column C1 & Beam D1(unit: kN-m)
Element
Solution I
Solution II
Solution III
N
2928
3694
3768
C1
Mx
273
21
20
story 1
N
4662
3694
3768
My
131
3.98
3.65
N
1643
2027
1724
C1
Mx
38
19
15
story 10
N
2923
1929
1591
My
207
5.48
5.26
M max
216
9.7
10.88
D1
Mmin
391
39.3
27.49
Võng
1.17
1.7
1.45

10 Vũ Quốc Anh, Phạm Ngọc Hiếu
Table 7. Stress in beam D1 & column C1 (Unit: daN-cm)
Element
Solution I
Solution II
Solution III
C1 (story 1)
589
3451
3516
C1 (story 10)
1139
3389
2873
D1
1414
2865
2149
Table 8. The mass of steel frames
The mass of steel
Solution I
Solution II
Solution III
(Tons)
870,8
388,3
401,1
4. Conclusion
The solution of using steel frame that is not directly connected to reinforced concrete wall
but connected to reinforced concrete floor can ease the processing of handling links, avoid stress
concentration or partial destruction or cracking of concrete at connecting locations.
Table 2: by using with the use of bracing, the stiffness of building is easily adjustable in two
different directions to be balanced.
The deformation of the building’s top (table 3 and 4): On X-axis, Staggered Truss Framing
Systems is not significantly effective in ensuring that the hardness of the building. The hardness
of the bulding is mainly ensured by the concrete core and some of columns and beams. The
displacement of solution 1 by X-axis is smaller than the two other solutions. Table 1 also shows
that the frequency f1 in the X-axis of three solutions are approximately equal, thus proven that
the Staggered Truss Framing Systems not have much effect in carrying the horizontal load.
Table 5 also indicated that in the X-axis the horizontal load is distributed mainly to the concrete
core. Table 2 presents the effect of outer braces in increasing the stiffness of the building so the
peak displacement of the two solutions (2 & 3) are significantly smaller than the first solution.
Table 5 shows that the outer braces on Y-axis distribute and carry the horizontal load across the
wall, thus the load exerted on the walls of the two solutions (2 & 3) is smaller than the first
solution.
- Table 6: The role of internal bracing helps distribute internal forces in the steel frame,
therfore moments in columns and beams of the two solutions (2 & 3) are very small and
remarkably smaller than solution 1.
- Table 7: stresses in beams and columns in solution 1 are small, while the two options (2 &
3) recorded large stress, hence applying solutions (2&3) takes advantage of high strength steel.
As for solution 1, although more stress excessed but it cannot reduce the cross section due to the
stiffness required by frame (frame peak displacement) and the deflection of the beam. Moreover
beam height in solution 1 is twice as much as two alternatives (solutions 2 & 3), thus increase the

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total height of the building. With the using of Staggered Truss Framing System, we can take
advantage of high-strength steel and reduce the floor's height navigation by reducing the beam
cross section.
- In solution II and III, the resulting cross internal forces and displacements of K-shaped or
X-shaped Staggered Truss Framing Systems are almost the same. This observation may help
architect to change between these two structure to assure the internal space required by the
building.
- Table 8 show that the amount of steel used in solution II and III decreased in compare with
solution I. The total amount of steel used in solution II reduced by 55% compared with solution
I. However, solution II needs additional cost for making Staggered Truss Framing Systems.
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Ministry of Construction (2006). Designing for building resistance earthquake load, TCXDVN
375:2006, Construction Publication, Hanoi.
Ph.D, P.E., S.E. Bungale S. Taranath (2012). Structural Analysis and Design of Tall
Buildings, Taylor & Francis Group, LLC.
An T.T (1996). Hỏi đáp thiết kế và thi công nhà cao tầng, Construction Publication, Hanoi.