High Rise Structures

• 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.

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

• 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.

• 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 behaviour.
• 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.

• Seismology (from the Greek seismos= 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.

• 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.

• P-waves
• \S-waves
• P-and/or S-waves.
• The two basic kinds of surface waves (Raleigh and Love).

• 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.

• 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.

1. Braced Frame
2. Rigid Frame Structure
3. Infilled Frame Structure
4. Flat Plate and Flat Slab Structure
5. Shear wall structure
6. Coupled wall structure
7. Wall-frame structure
8. Framed tube structure
9. The trussed tube
10. Tube in tube or Hull core structure
11. Bundled tube structure
12. Core and Outriggers system
13. Hybrid structure

• 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.

• 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.

• 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.
• 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 storiesonly; member proportions and materials cost become unreasonable for building higher than that.

• 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 soffit requiring the most uncomplicated formwork and, because of the soffit 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.
• 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.

• Tensile reinforcement for areas where tension stresses occur in walls when wind uplifts stresses exceeds gravity stresses.
• Compressive reinforcement with confinement ties where high compressive forces require the walls is designed as columns. Individual shear walls, say at the edge of a tall building, are design as blade walls or as columns resisting shear and bending as required.
• High strength concrete has enable wall thickness to be minimized, hence maximizing rentable floor space.
• Technology exists to pump and to place high-strength concrete at high elevation.
• Fire rating for service and passenger elevator shafts is achieved by simply placing concrete of a determined thickness.
• The need for complex bolted or side-welded steel connections is avoided.
• Well detail reinforce concrete will develop about twice as much damping as structural steel. This advantage where acceleration serviceability is critical limits state, or for ultimate limits state design in earthquake-prone area.

• Shear wall formed around elevator and service risers requires a concentration of opening at ground level where stresses are critical.
• Torsional and flexural rigidity is affected significantly by the number and the size of opening around the shear walls throughout the height of the building.
• Shear wall vertical movements will continue throughout the life of the building.
• Construction time is generally slower than for a steel frame building.
• The additional weight of the vertical concrete elements as compared to steel will induce a cost penalty for the foundations.
• An increase in mass will cause a decrease in natural frequency and hence will most likely produce an adverse affect of the acceleration response depending on the frequency range of the building. But shear wall systems are usually stiff and cause a compensating increase in natural frequency.

• A significant time lag will occur between footing construction and wall construction, because of the fabrication and erection on site of the moving formwork systems
• Time will be lost at the levels where wall are terminated or decrease in thickness, alignment of the shear walls are within tolerance.
• Regular survey check must be undertaken to ensure that the vertical and twist alignment of the shear walls are within tolerance.
• In general it is difficult to achieve a good finish from slip-form formwork systems, and hence rendering or some other type of finishing may be necessary.

Shear 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 centroidal 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.

Coupled shear walled 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 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 behaviour. 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 digitalisation serves to equalize the gravity loads of the exterior columns that give a significant impact on the exterior architecture.

• 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.

• 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.

• 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.

• The addition of expensive and labour-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.
• 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.

• 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.
• 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 under utilized. In some cases, outrigger systems can efficiently incorporate almost every gravity column into lateral load resisting system, leading to significant economies.

• Locating outrigger in mechanical and interstitial levels
• Locating outriggers in the natural sloping lines of the building profile
• Incorporating multilevel single diagonal outriggers to minimize the member?s interference on any single level.
• Skewing and offsetting outriggers in order to mesh with the functional layout of the floor space.
• Another potential drawback is the impact the outrigger installation can have on the erection process. As a typical building erection proceeds, the repetitive nature of the structural framing and the reduction in member sizes generally result in a learning curve which can speed the process along.