Structural buildings system and steel bracing

ENGINEERSTALK Structural System & Steel Building Bracing
High Rise Building Historical Brief
what is the structural system you need for your building
What is bracing
why we use bracing
what types of bracings
1
engineerstalkk@gmail.com . Eng.Abdulhakim Mawas 00966503898 abdulhakimmawas@yahoo.com

ENGINEERSTALK
High rise Buildings Historical brief
2
26Cent. BC
146m
73m-1368
Building Structural system

ENGINEERSTALK
3
16 cent. 500towers – 30meter

ENGINEERSTALK
4
Home insurance building
Chigaco -42 m-1884
Faltiron building 22 story steel
frame -1902

ENGINEERSTALK
Why high Rise Building
5

ENGINEERSTALK
1. Rigid frame
structural system
In rigid frame structure, beams and columns are
constructed monolithically to withstand moments
imposed due to loads.
The lateral stiffness of a rigid frame depends on the
bending stiffness of the columns, girders and
connections in-plane
20 to 25 story buildings can be constructed using
rigid frame system. For Concrete Building
6

ENGINEERSTALK
Advantages of rigid frame
1. Rigid frame
structural system
7

ENGINEERSTALK
2. Braced frame
structural system
engineerstalkk@gmail.com .
Types of High-Rise Buildings Structural Systems
Braced frames are cantilevered
vertical trusses resisting laterals
loads primarily diagonal
members that together with the
girders, form the “web” of the
vertical truss, with the columns
acting as the “chords’’.
Bracing members eliminate
bending in beams and columns.
8

ENGINEERSTALK
Types of High-Rise Buildings Structural Systems
2. Braced frame
structural system
9

ENGINEERSTALK
10

ENGINEERSTALK
Wall-frame system suitable for buildings
with storey number ranges from 40-60
storey which is greater than that of
shear or rigid frame separately.
braced frames and steel rigid frames
provide similar advantages of horizontal
interaction.
3. Wall-frame system (dual system)
11

ENGINEERSTALK
4. Shear wall system
It is a continuous vertical wall constructed from
reinforced concrete or masonry wall.
Shear walls withstand both gravity and lateral loads,
and it acts as narrow deep cantilever beam.
Commonly, constructed as a core of buildings
It is highly suitable for bracing tall buildings either
reinforced concrete or steel structure. This because
shear walls have substantial in plane stiffness and
strength.
Shear wall system is appropriate for hotel and
residential buildings where the floor-by floor repetitive
planning allows the walls to be vertically continuous.
12

ENGINEERSTALK
It may serve as excellent
acoustic and fire insulators
between rooms and
apartments.
shear wall structural
system can be
economical up to 35
stories building structure.
Shear walls need not to be
symmetrical in plan, but
symmetry is preferred in
order to avoid torsional
effects.
4. Shear wall system
13

ENGINEERSTALK
5. Core and
outrigger structural
system
Outrigger are rigid horizontal structures designed to improve
building overturning stiffness and strength by connecting the
core or spine to closely spaced outer columns
The central core contains shear walls or braced frames.
Outrigger systems functions by tying together two structural
systems (core system and a perimeter system), and render the
building to behave nearly as composite cantilever.
The outriggers are in form of walls in reinforced concrete
building and trusses in steel structures.
14

ENGINEERSTALK
5. Core and
system
15

ENGINEERSTALK
5. Core and
system
16

ENGINEERSTALK
Multilevel outrigger systems can provide up to five times the moment
resistance of a single outrigger system.
Practically, Outrigger systems used for buildings up to 70 stories.
Nonetheless, it can be used for higher buildings.
Not only does the outrigger system decline building deformations
resulting from the overturning moments but also greater efficiency is
achieved in resisting forces.
5. Core and
system
17

ENGINEERSTALK
6. Infilled frame structural system
Infilled frame structure system consists of beam and
column framework that some of the bays infilled with
masonry, reinforced concrete, or block walls.
Infill walls can be part-height or completely fill the
frame.
The walls may or may not be connected to the
formwork.
Great in plan stiffness and strength of the walls
prevent bending of beams and columns under
horizontal loads. As a result, frame structural
performance will be improved.
18

ENGINEERSTALK
During an earthquake, diagonal compression struts
form in the infills so the structure behaves more like a
Braced Frame rather than a Moment Frame.
It can build up to 30 story buildings.
19

ENGINEERSTALK
6. Infilled frame structural system
20

ENGINEERSTALK
7. Flat plate and
flat slab
structural system
This system consists of slabs (flat or plate) connected
to columns (without the use of beams).
flat plate is a two-way reinforced concrete framing
system utilizing a slab of uniform thickness, the
simplest of structural shapes.
The flat slab is a two-way reinforced structural system
that includes either drop panels or column capitals
at columns to resist heavier loads and thus permit
longer spans.
21

ENGINEERSTALK
Lateral resistance depends on the flexural stiffness of
the components and their connections, with the slab
corresponding to the girder of the rigid frame.
Suitable for building up to 25 stories.
22

ENGINEERSTALK
8. Tube
structural system
This system consists of exterior columns and beams
that create rigid frame, and interior part of the
system which is simple frame designed to support
gravity loads.
The building behaves like equivalent hollow tube.
It is substantially economic and need half of material
required for the construction of ordinary framed
buildings.
Lateral loads are resisted by various connections,
rigid or semi-rigid, supplemented where necessary by
bracing and truss elements.
23Structural Buildings Systems

ENGINEERSTALK
It is used for the construction of buildings up to 60
storeys.
Types of tube structure system include framed tube
system (fig.9), trussed tube system (fig.10), bundled
tube system (fig.11), and tube in tube system (fig.12).
Trussed tube system is formed when external bracing
added to make a structure stiffer. This structure type
suitable for building up to 100 storeys.
Bundled tube system consists of connected tubes
and it withstand massive loads.
A tube-in-tube system (hull core) is obtained, if the
core is placed inside the tube frame structure.
24
Structural Buildings Systems

ENGINEERSTALK
25

ENGINEERSTALK
8- tube system
26
Tube system types

ENGINEERSTALK
9. Coupled wall system This system composed of two or more
interconnected shear walls
Shear walls connected at the floor levels by beam or
stiff slabs.
Stiffness of the whole system is far greater than that
of its components.
The effect of the shear-resistant connecting
members is to cause the sets of walls to behave in
their partly as a composite cantilever, bending
about the common centroidal axis of the walls.
The system is suitable for buildings up to 40 storey
height.
Since planer shear walls support loads in their plane
only, walls in two orthogonal directions need to
withstand lateral loads in two directions.
27

ENGINEERSTALK
10. Hybrid structural
system It is the combination of two or more of basic structural
forms either by direct combination or by adopting
different forms in different parts of the structure.
Its lack of torsional stiffness requires that additional
measures be taken, which resulted in one bay
vertical exterior bracing and a number of levels of
perimeter vierendeel “bandages”
28

ENGINEERSTALK Structural Buildings Systems
29

30

31

32

ENGINEERSTALK Steel Building Bracing
Types of Bracing Systems Used in Multi-Storey Steel Structures
here are two major bracing systems:
Vertical bracing system
Horizontal bracing system
33

Vertical Bracing System for Multi-Storey Steel
Structures
Vertical bracing as shown in Figure-2 are diagonal
bracings installed between two lines of columns. Not
only does it transfer horizontal loads to the
foundations (create load path for horizontal forces)
but also it withstands overall sway of the structure.
Therefore, tensile diagonals provide necessary lateral
stability in addition to the floor beams that act as a
part of bracing system. Figure-2 shows the
placement of cross bracings between two lines of
columns.
34

As far as the single diagonal bracing is concerned, it
is designed to resist both tension forces and
compression forces. The arrangement of diagonal
bracing is illustrated in Figure-3.
35

Bracing elements are commonly placed at nearly 45
o because it not only offers an efficient system
compare with other systems but also strong and
compact connections between bracing member
and beam-column juncture will be achieved.
It is worth mentioning that, if the bracing member
inclination is smaller than 45o (angle from vertical),
then the sway sensitivity of the structure would be
increased whereas wider bracing member
arrangement provide greater structural stability.
36

What Are the Forces that Vertical Bracing Should Be
Designed to Resist?
Vertical bracing systems are required to be designed
to resist wind forces, equivalent horizontal forces that
represent the influence of initial imperfections and
second order effects caused by frame sway in the
case of the flexible frame.
37

How Many Vertical Bracing Planes Should be Installed?
It is recommended to provide at least three vertical bracing
planes to provide adequate resistance in both directions in plan
and against torsion forces around vertical axis of the structure.
If higher number of vertical planes of bracing is provided, it
would enhance structure stability. Practically, the number of
vertical plans of bracing is installed for multistory steel structures.
It is recommended to employ minimum two vertical planes of
bracing in each orthogonal direction to avoid disproportionate
collapse. Important part of the structure should be braced using
more than one plane of vertical planes to prevent progressive
collapse.
38

Locations of Vertical Bracing System in Multi-Story Structure
The location of vertical planes of bracing should be
determined carefully. It is advised to place the vertical
bracing planes at furthest point of the structure to withstand
torsion forces that may occur due to horizontal forces.
39

Horizontal Bracing System for Multi-Storey Steel Structures
Horizontal bracing systems purpose is the transfer of horizontal
loads from columns at the perimeter of the structure to the planes
of vertical bracing.
The horizontal forces on perimeter columns are generated
because of wind force pressure on the cladding of the structure.
There are two major types of horizontal bracing systems which are
used in the multistory braced steel structure namely: diaphragms
and discrete triangulated bracing
40

Regarding diaphragms, there are various types of
floor systems that some of them provide perfect
horizontal diaphragm such as composite floors
whereas others such as precast concrete slabs need
specific measures to satisfactory serve their purpose.
41

For example, steel work and precast concrete slab
should be joint together properly to avoid relative
movements.
As far as discrete triangulated bracing is concerned,
this type of bracing is considered when floor system
cannot be used as a horizontal bracing system.
42

t is a horizontal system of triangulated steel bracing
placed in each orthogonal direction. The horizontal
bracing are placed between supports which
commonly are locations of vertical bracings
Regarding bracing at roof level, wind girder is used
to resist horizontal forces at the top of the columns.
43

How to Choose Economical Steel Frames for Buildings and Structures?
There are various structural steel frame systems from
which designers can choose the most economical
type for specific building. The complexity and
economy of each frame system is different.
Different types of economical structural steel frames
include:
Braced frames in simple construction
Braced frames with continuous construction
Unbraced sway frames
Discrete stability frames
44

Braced Frames in Simple Construction
This steel frame type is the most economical and
least complex among other types. Braced frames
use simple beam to column connections.
It provides several advantages such as simplicity,
economical beam to column connection, columns
are small both in size and mass. Beams in this system
are subjected to sagging moments only, that is why
composite construction would considerably suitable
to be utilized.
45

Simple analysis can be used for the steel frame
because the structure is determinate that is why both
beams and columns can be easily optimized.
Apart from advantages provided, there are number
of disadvantages. For example, the beams in braced
frames will be costly if serviceability govern the
design of steel structure frame. It is not suitable
option for small scale structure when the design is
governed by strength.
46

The size of bracing element increases with the
increase the building height and number of story are
increased. This may make the bracing element
uneconomical. Therefore, it is necessary to
proportionate bracing elements carefully.
47

Braced Frames with Continuous Construction
This type of steel frame is economically suitable for the case where stiffness of
floors controls the design. Considerations required to be accounted for are
the same as those of braced frames with simple construction.
Braced frame with simple construction is more economical than braced
frame with continuous construction.
48

Braced Frames with Continuous Construction
Finally, beams and columns cannot be optimized
due to complex analysis method that is suitable for
such system.
One of the most outstanding benefits of braced
frames with continuous construction is that stiffness of
floor system is considerably improved due to
continuous beam to column connections.
However, continuous beam to column connection is
uneconomical and mass of external columns should
be considerably large to be able to withstand
imposed moments.
49

Unbraced Sway Frames
Un-braced sway frame system as shown in Figure-4 is considered
when bracing system cannot be used because it is not possible
architecturally.
So, either partially rigid or continuous steel frame system should be
used to resist horizontal forces. But it should be kept in mind that the
construction of semi rigid frame is considerably costly.
Moreover, the complexity and cost of un-braced sway frame is
greater than both braced with simple construction and braced with
construction frame. To make the un-braced sway frames
economical, it is required to size the structural elements properly.
50

Unbraced Sway Frames
Architectural configuration can be established
without the use of bracing elements. Despite this
advantage, there are certain disadvantages that
should be considered by designers.
For instance, beam to column connection is neither
simple nor economical, external columns with
substantial masses should be utilized to withstand
applied moments, and the size of structural steel
elements cannot be optimized easily because the
analysis is considerably complicated.
51

Discrete Stability Frames
It is considered to be the most uneconomical and
complicated steel frame type compared with others
explained above.
Architecturally, strong discrete stability frame is
favorable to withstand horizontal forces and provide
adequate stability.
It is necessary to use substantially strong beams and
columns because discrete stability frame must offer
complete and sufficient sway stiffness and sway
resistance.
52

When discrete stability frames are considered, then
strong columns need to support applied moments
and beam to column connections may be reduced.
Consequently, more economical frame would be
constructed compared with case where the entire
frame structure is assigned to resist horizontal force
because all beams and columns should be strong in
this case.
53

Moreover, architectural configurations can be established
without triangulated bracing. Beam to column connections in
partialized frame are costly and complex.
The size of steel elements cannot be optimized due to
complexity of the analysis used. Masses of external columns in
partialized frame should be substantially large to be able to
withstand the moment.
54

55

56

57

58

59

60

61

62
X-BRACED FRAME:
An X-braced frame (Fig. 1(a)) has
bracing members in tension for both
directions of loading, and if these are
sized to yield before the columns or
beams fail, ductility can be
developed.

63
DIAGONAL BRACES:
Single bays of diagonal braces (Fig. 1(b) and (c)) respond differently
according to the direction of loading. Configuration (b) may be much
weaker and flexible in the direction causing compression in the braces,
while configuration (c) will be weaker and more flexible in the storeys with
compression braces, leading to the possibility of soft-storey formation.
This is clearly not satisfactory. With more than one diagonally braced bay,
the performance can revert to that of X-bracing if a suitable arrangement of
bracing direction is chosen. Eurocode 8 requires a balance of compression
and tension braces at each level.
K-BRACES:
The same out-of-balance force applies to K-braces (Fig. 1(f )) when
the braces reach their capacity, but this time it is a much more
dangerous horizontal force applied to a column – dangerous
because column failure can trigger a general collapse. For this
reason, K-braces are not permitted
in seismic regions.

64
DIAGONAL BRACES:
Single bays of diagonal braces (Fig. 1(b) and (c)) respond differently
according to the direction of loading. Configuration (b) may be much
weaker and flexible in the direction causing compression in the braces,
while configuration (c) will be weaker and more flexible in the storeys with
compression braces, leading to the possibility of soft-storey formation.
This is clearly not satisfactory. With more than one diagonally braced bay,
the performance can revert to that of X-bracing if a suitable arrangement of
bracing direction is chosen. Eurocode 8 requires a balance of compression
and tension braces at each level.

engineerstalkk@gmail.com . abdulhakimmawas@yahoo.com 00966503898058
Steel Building Bracing
65

Structural buildings system and steel bracing

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Structural buildings system and steel bracing

Similar to Structural buildings system and steel bracing (20)

Recently uploaded

Recently uploaded (20)

Structural buildings system and steel bracing