بسم الله الرحمن الرحيم

بسم الله الرحمن الرحيم

HIGHRISE STRUCTURES By 1.MOHAMEDAYMAN 2.MOHAMEDELSAYED 3.MOHAMED ATEF 4.MOHAMED ALI Under supervision of : prof. Ahmed Kamal

contents • Introduction. • LOADS ON THE HIGHRISE STRUCTURES • Type of High-Rise Structure • Conclusion.

High-rise structure • high-rise is a tall building or structure. • • Buildings between 75 feet and 491 feet (23 m to 150 m) high are considered high-rises. • Buildings taller than 492 feet (150 m) are classified as skyscrapers.

The materials used • • The materials used for the structural system of high-rise buildings are reinforced concrete and steel. • Most American styleskyscrapers have a steel frame, while residential tower blocks are usually constructed out of concrete.

Main features of High-rise structures • • High-rise structures have certain features. The structures are high & lead to higher vertical loads and higher lateral loads (mainly due to wind stress) in comparison with lower buildings.

LOADS ON THE HIGHRISE STRUCTURES • Vertical Loads: • • Dead loads arise from the weigh to the individual construction elements and the finishing loads. • • Live loads are dependent on use depending on the number of stories; live loads can be reduced for load transfer and the dimensioning of vertical load-bearing elements. • · However, the reduction of the total live load on a construction element may not exceed 40%.

Horizontal Loads: • Calculation of lateral loads should be carefully scrutinized. • It generally arises from unexpected deflections, wind and earthquake loads

Unexpected Deflections • It arises from imprecision in the manufacture of construction elements and larger components. • • Another cause is the uneven settling of the foundation at an in-homogeneous site. • • Any deflection produces additional lateral forces.

Wind Loads • • High-rise buildings are susceptible to oscillation. It should not be viewed as statically equivalent loads, but must be investigated under the aspect of sway behavior. • • Wind tunnel experiments are used to see the influence of the building's shape on the wind load. • • The ability of wind loads to bring a building to sway must also be kept in mind. This oscillation leads both to a perceptible lateral acceleration for occupants, and to a maximum lateral deflection

Earthquake Loads • Definition: • • Seismology (from the Greek seism's= earthquake and logos= word) • • scientific study of earthquakes • • propagation of elastic waves through the Earth. • • studies of earthquake effects, such as tsunamis • • diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes such as explosions

Earthquake • • Produce different types of seismic waves. • • It travel through rock, and provide an effective way to image both sources and structures deep within the Earth.

Seismic Waves • • There are three basic types of seismic waves in solids: • • Pressure waves • • Shear waves • • Pressure and/or Shear waves. • • The two basic kinds of surface waves (Raleigh and Love).

Pressure waves • • Travel at the greatest velocity within solids and are therefore the first waves to appear on a seismogram. • • P-waves are fundamentally pressure disturbances that propagate through a material by alternately compressing and expanding (dilating) the medium, where particle motion is parallel to the direction of wave propagation.

Shear waves • • Transverse waves that travel more slowly than P-waves and thus appear later than P-waves on a seismogram. • • Particle motion is perpendicular to the direction of wave propagation. Shear waves do not exist in fluids such as air or water.

Type of High-Rise Structure • Braced Frame • Rigid Frame Structure. • In-filled Frame Structure • Flat Plate and Flat Slab Structure • Shear wall structure • Coupled wall structure • Wall-frame structure • Tube in tube or Hull core structure • Bundled tube structure • Core and Outriggers system • Hybrid Structure

Braced Frame • Braced frames are cantilevered vertical trusses resisting laterals loads primarily through the axial stiffness of the frame members. • • The effectiveness of the system, as characterized by a high ratio of stiffness to material quantity, is recognized for multi-storey building in the low to mid height range. • • Generally regarded as an exclusively steel system because the diagonal are inevitably subjected to tension for or to the other directions of lateral loading. • • Able to produce a laterally very stiff structure for a minimum of additional material, makes it an economical structural form for any height of buildings, up to the very tallest.

Advantages of Braced Frame • • Girders only participate minimally in the lateral bracing action-Floor framing design is independent of its level in the structure. • • Can be repetitive up the height of the building with obvious economy in design and fabrication.

Disadvantages of Braced Frame • • Obstruct the internal planning and the locations of the windows and doors; for this reason, braced bent are usually incorporated internally along wall and partition lines, especially around elevator, stair, and service shaft.-Diagonal connections are expensive to fabricate and erect

Rigid Frame Structure • Consist of columns and girders joined by moment resistant connections. Lateral stiffness of a rigid frame bent depends on the bending stiffness of the columns, girders, and connection in the plane of the bents. Ideally suited for reinforced concrete buildings because of the inherent rigidity of reinforced concrete joints. Also used for steel frame buildings, but moment-resistant connections in steel tend to be costly. While rigid frame of a typical scale that serve alone to resist lateral loading have an economic height limit of about 25 stories, smaller scale rigid frames in the for of perimeter tube, or typically rigid frames in combination with shear walls or braced bents, can be economic up top much greater heights.

Advantages of Rigid Frame Structure • • May be place in or around the core, on the exterior, or throughout the interior of the building with minimal constraint on the planning module. • • The frame may be architecturally exposed to express the grid like nature of the structure.

Advantages of Rigid Frame Structure • The spacing of the columns in a moment resisting frame can match that required for gravity framing.-Only suitable for building up to 20 –30 stories only; member proportions and materials cost become unreasonable for building higher than that.

In-filled Frame Structure • • Most usual form of construction for tall buildings up to 30 stories in height Column and girder framing of reinforced concrete, or sometimes steel, is in-filled by panels of brickwork, block work, or cast-in-place concrete. Because of the in-filled serve also as external walls or internal partitions, the system is an economical way of stiffening and strengthening the structure. The complex interactive behavior of the infill in the frame, and the rather random quality of masonry, has made it difficult to predict with accuracy the stiffness and strength of an in-filled frame.

Flat Plate and Flat Slab Structure • • Is the simplest and most logical of all structural forms in that it consists of uniforms slabs, connected rigidly to supporting columns. • • The system, which is essentially of reinforced concrete, is very economical in having a flat soft requiring the most uncomplicated formwork and, because of the soft can be used as the ceiling, in creating a minimum possible floor depth. • • Lateral resistance depends on the flexural stiffness of the components and their connections, with the slab corresponding to the girder of the rigid frame.

Flat Plate and Flat Slab Structure • • Particularly appropriate for hotel and apartment construction where ceiling space is not required and where the slab may serve directly as the ceiling. • • Economic for spans up to about 25 ft (8m),above which drop panels can be added to create a flat-slab structure for span of up to 38 ft (12m). • • Suitable for building up to 25 stories height.

Shear wall structure • Concrete or masonry continuous vertical walls may serve both architecturally partitions and structurally to carry gravity and lateral loading. Very high in plane stiffness and strength make them ideally suited for bracing tall building Act as vertical cantilevers in the form of separate planar walls, and as non-planar assemblies of connected walls around elevator, stair and service shaft. well suited to hotel and residential buildings where the floor-by floor repetitive planning allow the walls to be vertically continuous and where they serve simultaneously as excellent acoustic and fire insulators between rooms and apartments. Minimum shrinkage restraint reinforcement where the wall stresses are low, which can be for a substantial portion of the wall.

Coupled wall structure • • Consist of two or more shear walls in the same plane, or almost the same plane, connected at the floor levels by beam or stiff slabs. • • The effect of the shear-resistant connecting members is to cause the sets of wall to behave in their partly as a composite cantilever, bending about the common centurial axis of the walls. • • Suited for residential construction where lateral-load resistant cross walls, which separate the apartments, consist of in-plane coupled pairs, or trios, of shear walls between which there are corridor or window openings. Besides using concrete construction, it occasionally been constructed of heavy steel plate, in the style of massive vertical plate or box girders, as part of steel frame structure.

Wall-frame structure • The walls and frame interact horizontally, especially at the top, to produce stiffer and stronger structure. The interacting wall-frame combination is appropriate for the building in the 40 –60 story range, well beyond that of rigid frames or shear walls alone. • • Carefully tuned structure, the shear of the frame can be made approximately uniform over the height, allowing the floor framing to be repetitive. Although the wall-frame structure is usually perceived as a concrete structural form, with shear wall and concrete frames, a steel counterpart using braced frames and steel rigid frames offers similar benefits of horizontal interaction. • • The braced frames behave with an overall flexural tendency to interact with the shear mode of the rigid frames.

The trussed tube • The trussed tube system represents a classic solution for a tube uniquely suited to the qualities and character of structural steel. • • Interconnect all exterior columns to form a rigid box, which can resist lateral shears by axial in its members rather than through flexure. • • Introducing a minimum number of diagonals on each façade and making the diagonal intersect at the same point at the corner column. • • The system is tubular in that the fascia diagonals not only form a truss in the plane, but also interact with the trusses on the perpendicular faces to affect the tubular behavior. This creates the x form between corner columns on each façade. • • Relatively broad column spacing can resulted large clear spaces for windows, a particular characteristic of steel buildings. • • The façade digitalization serves to equalize the gravity loads of the exterior columns that give a significant impact on the exterior architecture.

Tube in tube or Hull core structure • This variation of the framed tube consists of an outer frame tube, the “Hull,” together with an internal elevator and service core. • • The Hull and core act jointly in resisting both gravity and lateral loading. • • The outer framed tube and the inner core interact horizontally as the shear and flexural components of a wall-frame structure, with the benefit of increased lateral stiffness. • • The structural tube usually adopts a highly dominant role because of its much greater structural depth.

Bundled tube structure • The concept allows for wider column spacing in the tubular walls than would be possible with only the exterior frame tube form. • • The spacing which make it possible to place interior frame lines without seriously compromising interior space planning. • • The ability to modulate the cells vertically can create a powerful vocabulary for a variety of dynamic shapes therefore offers great latitude in architectural planning of a tall building.

Core and Outriggers system • • Outrigger serve to reduce the overturning moment in the core that would otherwise act as a pure cantilever, and to transfer the reduced moment to columns outside the core by the way of tension-compression coupled, which take advantage of the increase moment arm between these columns. • • It also serves to reduce the critical connection where the mast is stepped to the keel beam. • • In high-rise building this same benefit is realized by a reduction of the base core over-turning moments and the associated reduction in the potential core uplift forces.

Core and Outriggers system • • In the foundations system, this core and outrigger system can lead to the need for the following: • • The addition of expensive and labor-intensive rock anchors to an otherwise “simple” foundation alternative such as spread footing. • • Greatly enlarged mat dimensions and depth solely to resist overturning forces. • • Time-consuming and costly rock sockets for caisson systems along with the need to develop reinforcement throughout the complete caisson depth.

Core and Outriggers system • • Expensive and intensive field work connection at the interface between core and the foundation. This connection can become particularly troublesome when one considers the difference in construction tolerances between foundations and core structure. • • The elimination from consideration of foundation systems which might have been nsiderably less expensive, such as pile, solely for their inability to resist significant uplift.

Advantages of Core and Outriggers system • The outrigger systems may be formed in any combination of steel, concrete, or composite construction. • • Core overturning moments and their associated induced deformation can be reduced through the “reverse” moment applied to the core at each outrigger intersection. This moment is created by the force couple at the exterior columns to which the outrigger connect. It can potentially increase the effective depth of the structural system from the core only to almost the complete building.

Advantages of Core and Outriggers system • Significant reduction and possibly the complete elimination of uplift and net tension forces throughout the column and the foundation systems. • • The exterior column spacing is not driven by structural considerations and can easily mesh with aesthetic and functional considerations. • • Exterior framing can consist of “simple” beam and column framing without the need for rigid-frame-type connections, resulting in economies. • • For rectangular buildings, outriggers can engage the middle columns on the long faces of the building under the application of wind loads in the more critical direction. In core-alone and tubular systems, these columns which carry significant gravity load are either not incorporated or underutilized. In some cases, outrigger systems can efficiently incorporate almost every gravity column into lateral load resisting system, leading to significant economies.

Disadvantages of Core and Outriggers system • The most significant drawback with use of outrigger systems is their potential interference with occipital and rentable space.

Hybridstructure • Combination of two or even more of basic structural forms either by direct combination or by adopting different forms in different parts of the structure. This systems provide in-plane stiffness, its lack of Torsional stiffness requires that additional measures be taken, which resulted in one bay vertical exterior bracing and a number of level of perimeter Vierendeel “bandages” –perhaps one of the best examples of the art of structural engineering. • Hybrid structures are likely to be the rule rather than the exception for future very tall buildings, whether to create acceptable dynamic characteristics or to accommodate the complex shapes demanded by modern architecture. High-strength concrete, consist of stiffness and damping capabilities of large concrete elements are combined with the lightness and constructability of steel frame exhibits significantly lower creep and shrinkage and is therefore more readily accommodated in a hybrid frame.

بسم الله الرحمن الرحيم

بسم الله الرحمن الرحيم

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