The application of the Steel materials in large-span cantilever composite structure

The application of the Steel materials in large-span cantilever composite structure
Nan Geng1.a
1College of Architecture and Civil Engineering of Taiyuan University of Technology ,Taiyuan
030024,China;
[email protected]
Keywords: Large-span cantilever, Behaviour analysis, Glass curtain wall, Steel materials
Abstract. The characteristic of the Steel materials are high strength, light weight, high integral
rigidity, high deformation capacity, So the Steel materials is suitable used to build large-span,
superelevation, extra-heavy type of building. The urban planning exhibition hall of cultural activity
center in Shanxi is large-span cantilever composite structure,that is SRC column and steel beam +
concrete frame structure, the maximum cantilever length of fourth layer truss is 10 m.Through the
top of the cantilever steel beam with its lower suspension truss and cross-section cantilever steel
beam of the first floor cantilever beam realize cantilever togetherly. Realize the structure design
based on Performance Analysis by using midas/gen ver8.00 to establish a rational model,. The pipe
truss and tensed cable structure joint control the total displacement of glass curtain wall.
Introduction
In order to promote the architecture of personality, special-shaped and large cantilever structures are
more and more. These more architectures are use of steel structure, such as large span cantilevered
steel structure of public fitness center in Dalian city[1]. Glass curtain wall is a new type of
contemporary wall. It endows the building with the biggest characteristic, that organically unify
architectural aesthetics, building function, building energy efficiency and building structure factors.
Grand magnificent glass curtain wall were constructed in the world's major cities of all the
continents,such as the New York world trade center, Hong Kong bank of China tower
Some urban planning exhibition hall of a cultural activity center in Shanxi province is large-span
cantilever glass curtain wall mixed structure (Fig. 1). In this paper, the structure was analyzed.
Based on the structure analysis and research,design points of the kind of long-span cantilever glass
curtain wall structure was deflection control of cantilever end and stress control of cantilever
element.
Advanced Materials Research Online: 2013-01-11 ISSN: 1662-8985, Vol. 644, pp 353-357 doi:10.4028/www.scientific.net/AMR.644.353 © 2013 Trans Tech Publications, Switzerland
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Project Summary
This structure is underground one layer,the earth four layers. The part of concrete structure column
size is 8.4m×8.4m,plane size is 42m×42m. Each story height is 5 m.Top level elevation is 19.950 m.
Concrete structure peripheral subsidiary of glass curtain wall modelling is irregular polygon. Roof
top elevation is 23.950 m. The most distant cantilever distance of glass curtain wall is 10 m.
Important selection of design parameters as follows:design working life is 50 years, safety classes
of building structures is II, classification for earthquake-resistance of building is C-class, earthquake
intensity is 8 degrees, venues is III class, classification of design earthquake for a group of frame
structure seismic is grade two, design basic acceleration of ground motion is 0.20 g. Reference wind
pressure is 0.4 kn/m2,reference wind pressure is 0.25 kn/m2.
The Structure Arrangement and Design Characteristics
Superstructure. The project is composite structure. In order to guarantee reliable connection of
cantilever part and the main structure, the cantilever side of main structure from underground a
layer to fourth layer column use steel reinforced concrete. The First floor cantilever platform, the
four-storey cantilever beam and diagonal brace use the welded steel H-section, hot rolled H-shaped
steell. South side of glass curtain wall structure use square steel tube, round steel pipe and cable.
Roof use pipe truss structure.
According to the size of the glass, layout the main beam and secondary beam of the second-floor
cantilever platform. Shape of glass curtain wall from the First flool to the four-storey is irregular,
using the pipe truss forms architectural modeling.Curtain wall is plane, in order to ensure structural
lateral stiffness uses tension cable structure. According to the architectural modeling, roof use
longitudinal and lateral four pipe truss.
Structural Irregularity Judgement. Vertical regularity: level stiffness ratio of the first is less than
the second 95%, the lateral stiffness of is irregular[2] .
Size mutation: Maximum distance of the second cantilever is 8 meters, which is more than 4 m limit
with level cantilevering size specified by code .
Structure Design Key and Structural Measures
Design Key Points. The length of the Second cantilever is 4 ~ 8 m. Building function of platform is
exhibition hall,which uses toughened glass as the ground material.The load of Platform is
bigger.According to the Technical Code for Glass Curtain Wall Engineering[3],the absolute
deflection of glass curtain wall should not be more than 20 mm. So the vertical displacement of the
second cantilever glass platform was controled within 20 mm, this could avoid bigger deflection
producing ground glass damage.
The glass curtain wall of the structureelevation is relatively complicated,and curtain wall vertical
and horizontal displacement should are controlled within 20 mm. When designing use truss and
tensed cable structure to control the displacement.
Structure Measures with View of the Above Key. In the analysis,the following two schemes
were compared. Scheme 1:The first cantilever platform was self cantilever platform.Vertical truss
and tensed cable structure only beared self-weight of curtain wall, which did not share platform load.
Scheme 2: Vertical truss, tensed cable structure and the first cantilever platform which was
connected by vertical truss and tensed cable structure shared the first platform load, showed Fig 2.
By building scheme was restricted, clear height of the first cantilever platform was controled in less
354 Advanced Research on Intelligent Systems and Mechanical Engineering
than 1.5 m.Scheme 1 depending solely on platform their stiffness could not controlled displacement,
maximum vertical displacement of platform getted 49 mm.Scheme 2 could realized control of
displacement, maximum vertical displacement of platform getted 19 mm. Internal force contrast
of cantilever beam in scheme 1 and scheme 2 show Table 1. Scheme 2 larger reduced the internal
force of steel beam , which was beneficial for steel beam.
Table 1 Scheme 1 and scheme 2 cantilever beam root internal force contrast
Cantilever beam
(kn)
5 axis 7 axis 9 axis 11 axis 5 axis 7 axis 9 axis 11 axis
Scheme 1 119 1382 1012 353 81 291 261 119
Scheme 2 156 674 618 424 117 170 170 175
According to the Technical Code for glass curtain wall engineering,the absolute deflection of glass
curtain wall should not be more than 20 mm. This structure's glass curtain wall shape is irregular. In
curtain wall outside convex part, using the steel truss can form building modelling. The truss also
can increase the structural lateral stiffness, and resist wind load. Plane of the curtain wall in the
medial set BBS, in order to increase the lateral stiffness. Through truss and tensed cable structure
common controls curtain wall displacement, showed Fig 4.
To make all lower boom of the vertical truss are tension member, and avoided the emergence of
compression member, adjusted section of four variable cross-section beam connecting with steel
reinforced concrete column. Along with cantilever distance increasing, increased section of beam to
increase the stiffness of beam. Through the comparison of the schemes, beam section are
respectively H1000~400×400×16×30, H800~400×400×16×30, H800~400×400×16×30,
H400×400×16×30.
In order to control displacement and stress of the steel ratio of the cantilever beam end , increase a
root braced steel beam supporting to three layer beam-column junction.In order to increase the steel
braced safety reserve, when designing brace of stress ratio control below 0.4.To increase torsional
rigidity of top cantilever beam, increased level support in the plane of 7, 9 axis diagonal brace.
Advanced Materials Research Vol. 644 355
Glass roof in the overhang and overhanging beam use of welded connections, which can further
increase of steel vertical rigidity, and reduce the vertical displacement of the curtain wall and the
platform.
Glass curtain wall was lifted on the beam end through nodes (showed in Fig.8). In order to
guarantee the safety of nodes, the number of the bolt will be increased to 4 times, at the same time
in the square steel tube side increase axillary with an extended weld connection length.
The site splicing of overhanging beam, considered the seismic full stress design methods, used of
plug welding mixed connection[4].
Structure Elastic Analysis
Multi-earthquake Design Load Combination. Design load combinations consider varieties of
combinations among constant load, live load, wind load, X to the earthquake action, Y to the
earthquake effect, and vertical seismic action.
Glass curtain wall belongs to non-load-bearing peripheral protection structure, the structure is
mainly considered their own safety. The structure of the glass curtain wall and top glass roof shape
are irregular. In Load code of the design of building structure can not find the corresponding wind
load shape coefficient, so the wind load value can't be accurately calculated. In the design the wind
load calculation used of estimation and amplification method. If you want to calculate the structure
of the accurate wind load, need to undertake building wind tunnel test, or simulate the structure of
the wind load by using wind load CFD numerical. The wind load calculation of this complex shape
would be further discussed.
Calculation Content and the Program. According to the standard requirement the whole internal
force and displacement of the structure were calculated under multi-earthquake earthquake. Using
MIDAS/GEN Ver8.00 established reasonable finite element model of this structure and calculated
the internal force and displacement under multi-earthquake. Frame structure section used the beam
element, plate unit and wall units. The roof of pipe truss structure and glass curtain wall structure
used beam element and truss element. There were 13871 units of the model. Structural calculation
model was shown in Fig 3. The structure was combination structure of concrete structure and steel
structure. So the group damping ratio calculation method was used when modeling.
MIDAS Overall Analysis Results. MIDAS analyze the original frame structure and the combination
structure. Period ratio, maximum storey drift, he structure whole stability, participating mass ratio
can meet the requirements of specification.The period and frequency of the original frame structure
and the combination structure are comparing analyzed .It is benefit for original structure after
Increasing steel structure,
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Table 2 The original frame structure and composite structure period and frequency comparison
The original frame construction
translation 1 1.094 0.914
Conclusion
1. The structure made by steel materials is one of the main building structure types.The
characteristic of the Steel materials are high strength, light weight, high integral rigidity, high
deformation capacity, so the steel materials is suitable used to build large-span, superelevation,
extra-heavy type of building.Steel structure is more easy to realize complex building.
2. MIDAS software was used for X-way, Y-way and vertical earthquake action of this structure to
carry on the calculation.Through calculation, the structure satisfy the existing standard requirement.
3. According to the checking computations, the project achieves the expected performance target,
envelope design when specific design according to the performance target can meet the standard
requirement.
4. The structure of the body is relatively complicated. If want to calculate the the accurate wind load
of structure, need to undertake building wind tunnel test, or use wind load CFD numerical
simulation the structure of the wind load. The wind load calculation of this complex shape would be
further discussed.
References
[1] S. Li and S.G.Qiu: Performance-based design of large-span cantilever structure and research of
the penetrated joint in Dalian Citizen Sports Center testing in the reinforcement of the structure
of the fire damage. Building Structure .2011.(In Chinese)
[2] Code for seismic design of buildings GB50011-2010 China Architecture & Building Press 2010
[3] Technical Code For Glass Curtain Wall Engineering JGJ102-2003.China Architecture &
Building Press 2003.
[4] Handbook For Design Of Steel Structures.China Architecture & Building Press 2012.
Advanced Materials Research Vol. 644 357
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