Lateral Load Resisting Systems
Lateral Load Resisting Systems
Lateral Load Resisting Systems
Deformed Shape
2-In Filled Frames:
The in filled-frame is common in Europe for building up to 30
stories in height.
The reinforced concrete frame of columns and girders is in-filled by
panels of brickwork, block-work or cast-in-place concrete.
When subjected to lateral load, the infilled frame acts as a strut
along the compression diagonal to brace the frame.
The random flow of lateral loads makes the infilled frame difficult
to analyze. In addition, the possible removal of walls by future
tenants may weaken the frame in unpredictable ways.
3-Shear walls:
The shear walls are primary lateral load resistance.
Shear walls act as vertical cantilevers, typically around elevator,
stairs and service shafts.
Shear wall are stiffer than rigid frames and are economical to about
55 stories.
When shear wall are combined with frames, the wall attract all
lateral loads, so the frames is designed only for gravity.
3-Shear walls(cont.):
The deformed shape of the
Shear Wall system system
shows that the Wall has a
high rigidity in the Lower
floors where there is a
little deformation more
than the Higher floor.
Deformed Shape
4-Shear Wall-frame Structures:
Wall-frame structure is a combination of shear walls and rigid frames.
The structure is constrained to adopt a common deflected shape to
both systems through the horizontal rigidity of the girders and slab.
Combining the two systems in tall buildings:
The shear walls (flexural deflection) will dominate the lower levels.
The frames (shear deflection) will dominate the upper levels
The combination increases the economy of height to the 65 story
range, well above the range of rigid frames or shear walls alone.
4-Shear Wall-frame Structures(Cont.):
5-Shear Wall Frame Interaction With
Haunched Girder:
The Haunched girder Just enhance the shear wall frame interaction by
better transition of straining action between the shear wall and the frame.
The Haunched girder system makes a better
distribution of straining action between frame
and shear wall. Hence, drift get decreased and
straining action better distributed.
6-Outrigger-Braced Structures:
This system consists of a central braced core, which is either a
braced frame or shear walls, plus horizontal cantilever “outrigger”
trusses or girders that connect the core to the outer columns
When the structure is loaded horizontally, the vertical plane
rotations of the core are restrained by the outriggers through tension
in the windward column and compression in the leeward column.
The effective structural depth of the building is greatly increased,
thereby augmenting its lateral stiffness and reducing the lateral
deflections and the moments in core
The outrigger system has been used to 70 stories in height.
6-Outrigger-Braced Structures(Cont.):
6-Outrigger-Braced Structures(Cont.):
The outrigger makes a better The outrigger
distribution of straining
actions between core and
shear wall or frames.
The outrigger system also
decreases the total drift of A core inside
the building. the building
Using another outrigger in
the lower floors will enhance
the distribution of straining
actions
6-Outrigger-Braced Structures(Cont.):
7-Framed-Tube Structures:
The essence of the framed-tube is the very stiff moment-resistance
frames that form the tube around the perimeter of the building.
The frames consist of closely spaced columns, typically 1.5 to 3.5m,
tied together by horizontal deep spandrel girders.
This close spacing must be interrupted at street level with the use of
transfer beams, or like the World Trade Center Building.
The outer tube carries 100% of the lateral loads, and 75 to 90% of the
gravity loads.
The remaining gravity load is carried by the small cluster of core
columns (or shear walls).
7-Framed-Tube Structures(Cont.):
Under lateral loads, the perimeter frames aligned in the direction
perpendicular of loading acts as the flanges.
The most efficient tube would be a square plan or a circular plan.
This structure form is suitable for both steel and reinforced concrete,
from heights of 45 to 110 stories.
This form is the most significant modern development in tall
buildings, although it needs improvement, because the flanges tend
to suffer from shear lag.
This shear lag is due to the mid-face flange columns being less
stressed than the corner columns.
7-Framed-Tube Structures(Cont.):
Shear Lag Phenomena in Tall Buildings:
Shear Lag Phenomena in Tall Buildings:
Shear Lag is the phenomena in which the stress
is unbalanced by concentration of stresses on the
edges with respect to the stresses on the other
parts of the stresses flange.
This shear lag effect reduces the effectiveness of
the box structure by increasing/decreasing the
stress concentration at the web flange junction,
reducing/increasing the axial stresses at the
middle of the frame panels, which accumulates
to increased lateral deflection of structure.
Shear Lag Phenomena in Tall Buildings:
Shear Lag is very High at the first
floors and get decreased in the upper
floors.
Reducing The Effect of Shear Lag: %
Effect of beam depth on Shear Lag
depth(cm)
7-Framed-Tube Structures(Cont.):
8-Tube in Tube Structures:
A variant of the framed-tube form is the replacement of the inner or core
columns and walls, with another tube.
The hull (or external tube) and the new core tube act jointly to resist both
gravity and lateral loads.
This improved form is called a tube-in-tube or a hull-core structure.
A steel building could provide a core tube made up of braced frames,
whereas a reinforced concrete building would consist of an assembly of
shear walls of the core.
The outer framed tube and the inner core interact horizontally as the shear
and flexural components of a wall- frame structure.
It is presumed that this form could push the height to an economical 120
stories.
8-Tube in Tube Structures(Cont.):