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Composite Structures Of Steel and Concrete 钢-混凝土组合结构

By Professor. Shiming Chen 2015

• Part 1 What are composite structures• Part 2 References & assessment• Part 3 Introduction to composite

structuresBasic structural components: composite beams composite slabscomposite columns

• What are composite structures（组合结构）?The structures consist of members of combining structural steel and concrete effectively.（型钢与混凝土的组合）

‘Composite construction’ Structural systems in which there is interaction between concrete and structural steel（钢与混凝土的共同作用）

• Why is composite construction?

Example 1

Composite beam

Non composite beam

Construction elements

composite column floor = beam + slabcomposite beam

composite slab

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Construction elements

Composite slabs

Reinforced concrete slab

in-situ concrete on shuttering partially prefabricated slabs fully prefabricated slabs

7

Construction elements

SlabsProfile steel sheeting

Interlock between steel and concrete

frictional mechanical

end anchorage8

• Composite construction is a product of recent design and construction practice, began just prior to the start of the twentieth century（20世纪初）.

• Many countries have their own stories to tell about composite construction.

• The first composite construction with design approval appeared in the year of 1894 when a bridge and a building were constructed in the USA, namely, the Rock Rapids Bridge in Rock Rapids, Iowa, and the Methodist Building in Pittsburgh.

• Many novel advantages: combining concrete and steel in the design of the primary structure for a high-rise building.

• Using the best properties of both materials to solve the design challenge can result in a cost-effective solution that best meets a project’s architectural and functional requirements.

Strictly composite :• interaction of two materials within one

construction element (e.g. a concrete-filled tubular steel column)

• the philosophy of mixed building technologyincludes the combination of construction elements or members built up with different construction methods (e.g. concrete column in combination with a composite beam and a prefabricated slab).

Introduction to Composite Construction

some applications.

Latitude at World square -Sydney

Latitude at World square -Sydney

Shanghai Tower in construction

Brief Introduction to Shanghai Tower• Location: Lujiazui Finance and Trade Zone, Pudong

district, Shanghai, China• Owner/Developer: Shanghai Tower Construction and

Development Co., Ltd.• Design Architect: Gensler• Local Design Institute: The Architectural Design &

Research Institute of Tongji University• Structural Engineers: Thornton Tomasetti• Mechanical, Electrical and Plumbing (MEP) Engineers:

Cosentini Associates• Date of Commence: Sep.18, 2010• Date of Anticipated Completion: Dec. 30, 2014

上海中心大厦结构体系特点

• 地上124层, 高632m, 采用巨型框架-核心筒-伸臂桁架抗侧力结构体系, 钢-混组合结构。

• 巨型框架结构由8根巨型柱、4根角柱以及8道位于设备层箱形空间环带桁架组成

• 核心筒为钢筋混凝土结构, 截面平面形式根据建筑功能布局由低区的方形逐渐过渡到高区的十字形；1~ 2区核心筒翼墙和腹墙中设置钢板, 形成了钢板组合剪力墙结构, 墙体中含钢率为115% ~ 410%

Composite floor

• Aims of the course To gain knowledge of composite structures

To master design principle of composite structures

To know key research/application topics in composite structures

To develop comprehensive understanding of steel and concrete composite construction via summarizing and reporting on the selected topics

Reference books• Composite Structures of steel and concrete:

Beams, Slabs, Columns, Frames for Buildings byR.P. Johnson Blackwell Publishing, 2004

• Composite Construction, by D. Nethercot, PronPress, 2004

• Steel and Concrete Composite Structures, LectureNotes by Shiming Chen, 2010

• 钢-混凝土组合结构, by 陈世鸣，中国建筑工业出版社，2013年

Chapter 1 Composite Construction- General

• OBJECTIVE/SCOPETo introduce steel-concrete composite

members and construction; to explain the composite action of the two different materials and to show how the structural members are used, particularly in building construction.

• 1.1 Why is composite construction• Traditional Structures for buildings:• Masonry structures• Wood structures• Steel structures• Steel reinforced concrete structures• Steel-concrete composite structures

(composite structures as brief)• Other composite materials (FRP)

Comparison with other methods

Alternative Steel Beam Types

In a composite floor system the concrete acts together with the steelto create a stiffer, lighter, less expensive structure (Allen 1999)

Metal Decking

Steel deck-concrete: composite construction

• Composite decking works together with the concrete fill to make a stiff, light-weight, economical floor system

• Composite decking is available in various profiles and thicknesses

Featues: Shear connector installation

• The additional subcontractor needed for shear connector installation willincrease field costs

• Installation of shear connectors is another operation to be included in theschedule

• A concrete flatwork contractor who has experience with elevated compositeslabs should be secured for the job

Basic forms of composite construction

Conventional and innovative

composite beams

Composite beams

1.2 Composite action in beams• Consisting of a steel section acting compositely

with concrete slab. The two materials are interconnected by means of mechanical shear connectors.

• A simply supported beams: under vertical loads, sagging bending moments cause tensile force in the steel section and compression in the concrete deck, optimum use of each material.At the steel/ concrete interface, mechanical shear connectors are provided to resist the horizontal shear.

If slip is free to occur, each component will act independently. If slip is eliminated, the slab and the steel member will act together as a composite unit.

Definitions for strength and stiffness properties• Complete and partial shear connection is regard

to the design bending strength of the beam other than the horizontal shear resistance

• Complete or incomplete interaction results in a more or less stiff composite beam

• Composite beams are designed using plastic design methods and partial interaction theory, combing steel and concrete to great effect

• Shear connectors are commonly referred to as“studs” or “shear studs” in the trade

• They are available in a range of sizes,materials, and grades

• Headed studs (as shown) are most commonlyused

Shear Connectors

Types of shear connectors

Shear connections

• Depending on the welding process used, the tip of theshear connector may be placed in a ceramic ferrule (arcshield) during welding to retain the weld

• Shear connectors create a strong bond between the steelbeam and the concrete floor slab which is poured on topof the metal decking

• This bond allows the concrete slab to work with the steelbeams to reduce live load deflection

Shear Connectors

Composite beams, subject mainly to bending, consist of a steel section acting compositely with one (or two) flanges of reinforced concrete

1.3 Composite floors or slabs• Composite floor: steel deck with additional

indentations or embossments acts as both permanent formwork during concreting and tension reinforcement after the concrete has hardened.

• Main advantages to the designer and client• speed and simplicity of construction• lighter construction than a traditional concrete• less on-site construction

high tolerances /under controlled factory conditions/ quality procedures.

Rquired composite action can be achieved if:a. Mechanical interlock be provided by

deformations in the steel profileb. Frictional interlock for profiles shapedc. End anchorage

Metal decking ready to be laid by hand

Edge trims for metal deck floor construction

Floors using metal decking which is embossed to provide composite action.

Composite slab

• As an alternative to welding, powderactuated tools may be used to attach metaldecking to structural steel

• Powder actuated tools use the expandinggases from a powder load, or booster, todrive a fastener

• A nail-like fastener is driven through themetal deck into the steel beam

• The powder actuated tool, powder load, andfastener must be matched to the thickness ofthe structural steel beam flanges

Installation of Decking

• Shear connectors are installed after the decking is in place

• Shear connectors may be installed by the steel erection contractor or aspecialty shear connector installer

• The welding equipment required for installation is provided by the shearconnector installer

• Daily output for shear connector installation averages about 1000 per daydepending on the size of the connectors (Means 2004)

Installation of Shear Connectors

• The electrical arc process is commonly used for stud welding An arc is drawn between the stud and the base metal The stud is plunged into the molten steel which is contained by the ceramic

ferrule The metal solidifies and the weld is complete

• The ferrules are removed before the concrete is poured(ASCE 2002, AWS 2004)

Installation of Shear Connectors

• There is an art to the placement of concrete on metal deck and structural steel

• The work, unless shoring is used, must be executed on a deflecting surface

• An experienced concrete contractor should be employed for this work

Concrete should be deposited over supporting members first, then spreadtoward the deck midspans

The accumulation of a deep pile of concrete must be avoided

(AISC 2003, ASCE 2002)

Installation of Concrete

• The contractor must be aware of camber in the beams and the expecteddeflections

• Consultation with the structural engineer may be necessary

• As the concrete cures it forms a connection with the composite metaldecking and shear studs

• The composite floor system is now complete

(AISC 2003)

Installation of Concrete

• The shear connectors used in composite construction require specificinspections and quality control

• Testing procedures are specified in the contract documents or by a localbuilding authority

• AWS D1.1 – Structural Welding Code – Steel, Section 7: Stud Welding(AWS 2004) specifies the tests and inspections for shear studs

Quality Control

• As described in the AWS code (AWS 2004), jobsite conditions may exist thatprohibit or delay the stud welding operation

• The primary issues affecting the installation of the shear connectors are:

Moisture on the decking or ferrules

Moisture between the decking and the steel beam below

A steel temperature below 0° F

• In the pictures above, a torch is being used to remove snow (left) from theareas where shear studs are to be installed (right)

Quality Control

• Required quality control procedures for shear connectors includepre-production tests and fabrication inspections

Pre-production testing is performed by the shear stud installer at thebeginning of each work shift and includes the following steps:

The stud installer performs visual fabrication inspections as studs areinstalled

Other testing may be specified or may be necessary if all visualinspections are not passed (SIN 1998)

1. Weld two sample studs

2. Inspect for flash

3. Perform bending test

4. Equipment settings are recorded

Quality Control

When used appropriately, typical overall building costs will be less forcomposite construction than non-composite construction

Cost Impacts of Composite Construction

• The duration for the installation of shear studs is project dependent andshould be considered on a project by project basis

• Shear stud installation usually has little or no impact on the overall projectschedule

Scheduling of Composite Construction

• It may be possible, depending on the size of the structure and the sequencingof erection and decking, to install the shear studs as erection proceeds

• It may also be possible to have a majority of the shear connectors in placeand begin placing concrete for the floor slabs while structural steel is beingerected in another area of the building

• On the structure shown above part of the composite first floor slab was placedwhile erection of the structural steel for the third floor proceeded

Scheduling of Composite Construction

1.4 Composite columns• Types of composite columns

concrete encase steel columns/concrete filled steel tube columns/rolled section column partly encased in concrete

Cross section of composite column

Tubular column with shot fired nails as shear connectorsand reinforcement on site

• Encased steel composite columns:Full composite interaction without any slip at the steel-concrete interface is assumed;The complete interaction must be ensured by means of mechanical connections.

Concrete-filled composite columns

• Steel sections: rectangular and circular tubes

• Complete interaction between the structural components of the column, through direct interface bond

Beam-to-Column Connection: vertical shear transferbetween beams and composite columns

1.5 Composite bridges• Medium-span composite bridges(from 35 m up

to 60 or 70 m) are normally constructed from welded, built up, steel plate girders and a wide reinforces concrete deck

• Smaller spans, from 20 up to 35 m, rolled steel sections are more popular

• Special considerations : during erection and concreting (usually without intermediate propping), during service life etc.

• 1.6 Advantages over the traditional reinforced concrete or steel structures:high strength-to-weight ratios; structural integrity; durable finishes; dimensional stability; sound absorption and etc.

One important argument: use of rolled steel sections, profiled metal decking and/or prefabricated composite members speeds up construction.

Example:

Steel framing supporting cast-in-place reinforced concrete slab construction was historically designed with no consideration given to the composite effect of the steel and concrete acting together.

In composite construction, mechanical shear connectors to resist the horizontal shear which develops during bending are provided, so that the load carrying capacity of the structure is increased.

Composite floor construction is highly competitive, if spans are increased to 12, 15 and even 20 m.

1.7 Development and applications• Before 1950s:Individual case of using the forms of combination

of steel/iron and concrete to prevent metal from corrosion and fire attackRecognition beneficial effects on strength and

stiffness in the structures with the combination: mainly: encased steel beams, encased steel columns, and concrete filled steel tubesApplication in reconstruction of bridges and

building destroyed in the second World War

• 1950s~1960s pioneer research carried out in UK, and in the United states

• 1960s~1980s applications in different countries• 1980+ composite structures were introduced into

Chinese construction practice, research and application

• Now combination of concrete cores, steel frame and composite floor construction has become the standard construction method for multi-story commercial buildings in several countries worldwide.

Composite construction in a high-rise hotel buildingMillennium Tower Vienna (Austria)

Composite construction in

high-rise commercial

building

Composite construction in

buildings

Citibank Duisburg (Germany)

Parking deck “DEZ” (Innsbruck-Austria)

Composite slab in construction stage

Beam-column joint

Composite construction applied in over-pass bridge

Prefabricated Composite Bridge

Box Girder Bridges over Majorsviken

Composite Girder with Corrugated Web 法国于1975年(CB公司)提出，86年建成Cognac桥。用弯成波折形状的薄壁钢板，来代替混凝土腹板，建成跨度31m+43m+31m、首座连续波折腹板组合箱梁桥。

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France: the Maupre Bridge (1987)

Maupre桥

Seven continuously seven span boxed girder，total length 325m，main span: 53.55m，deck breadth:10.75m。

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1.8 Concluding summary• Composite construction is popular for buildings

and bridges• Composite construction / rapid construction• Weight of steelwork required is significantly less

than if the materials were used independently• No need for expensive falsework and formwork• Using composite beams is more significant, for

medium-to-long spans than for short spans.• Disadvantages: provide connectors; complicated

than other methods to design and construct

• Review points:• Describe the main differences of steel-concrete

composite structures from (1) reinforced concrete structures (2) steel structures.

• Brief the advantages and disadvantages of composite structures.

• Find the applications of composite construction in building practice (composite beam/slab/column and etc.)