Basic Design Criteria for High Rise Buildings Design

1. Design criteria that need to consider for high rise buildings:
Presented By: Engr. Md. Arafat Hasan
Structural Engineer at Parent Construction & Consultancy Ltd.
The Basic Design Criteria:
1. Limit States Design Philosophy
2. The Speed of Erection
3. Loading
4. Sequential Loading
5. Strength and Stability
6. Drift Limitations
7. Stiffness
8. Human Comfort
9. Creep, Shrinkage, and Temperature effects
10. Fire
11. Foundation Settlement and Soil-Structure Interaction
1. Limit States Design Philosophy: The aim of this approach is to ensure that all
structures and their constituent components are designed to resist with reasonable
safety the worst loads and deformations that are liable to occur during construction
and service, and to have adequate durability during their lifetime. The entire
structure, or any part of it, is considered as having“failed”when it reaches any one
of various “limit states. “Two types of limit states must be considered: The
ultimate limit states, corresponding to the loads to cause failure, endangering lives
and causing serious financial losses, the probability of failure must be
low.Theserviceability limit states, which involve the criteria governing the service
life of the building. Since the consequences are not catastrophic, a much higher
probability of occurrence is permitted. A particular limit state may be reached as a
result of an adverse combination of random conditions. Partial safety factors are

2. employed for different conditions that reflect the probability of certain occurrences
or circumstances of the structure and loading existing. The implicit objective of
the design calculations is then to ensure that the probability of any particular limit
state being reached is maintained below an acceptable value for the type of
structure concerned
2. The Speed of ErectionProcess: The speed of elections a vital factor in
obtaining a return on the investment by minimizing the cost of interest payments
on the large capital costs involved in such large-scale projects. Most tall buildings
are constructed in congested city sites with difficult access, and with no storage
areas. Careful planning and organization of the construction sequence become
essential. The story-to-story uniformity of most multi-story buildings encourages
construction through repetitive operations and prefabrication techniques. The
progress in the ability to build tall buildings has gone hand in hand with the
development of more efficient equipment and improved methods of construction,
such as:-Slip-and flying-formwork-Concrete pumping-The use of climbing tower
cranes and large mobile cranes.
3. Loading: The structure must be designed to resist the gravitational and lateral
forces, both permanent and transient that will be sustained during construction and
during the expected useful life of the structure (from 60 to 100 years). These forces
will depend on the size and shape of the building, and its location. Load
combinations depend on the probable accuracy of estimating the dead and live
loads, and the probability of the simultaneous occurrence of different combinations
of gravity loading, both dead and live, with either wind or earthquake forces. The
accuracy of these loads is included in limit states design through the use of
prescribed factors.
4. Sequential Loading: For dead loads, the construction sequence should be
considered to be the worst case. It is usual to shore the freshly placed floor upon
several previously cast floors. The construction loads on the supporting floors due
to the weight of wet concrete and its formwork will greatly exceed the loads of
normal service conditions. These loads must be calculated considering the
sequence of construction and the rate of erection. However, the designer rarely
knows who the contractor will be, nor his method of construction. If column axial
deformations are calculated as though the dead loads are applied to the completed
structure, bending moments in the horizontal components (for example, beams)
will result from any differential column shortening. Because of the cumulative

3. effects of column axial deformations over the height of the building, the effects are
greater in the highest levels of the building. However, the effects of such
differential movements could be greatly overestimated because in reality, during
the construction sequence, a particular horizontal member is constructed on
columns in which the initial axial deformations due to the dead weight of the
structure up to that particular level have already taken place. The deformations of
that particular floor will then be caused by the loads that are applied subsequent to
its construction. Such sequential effects must be considered if an accurate
assessment of the structural actions due to dead loads is to be achieved.
5. Strength and Stability: The primary requirement of the ultimate limit state
design procedure is that the structure have adequate strength to resist and remain
stable under the worst probable loads during its lifetime. This includes all critical
load combinations, augmented moments from second-order deflections (P-delta)
plus an adequate reserve, study all critical members whose failure may lead to a
progressive collapse of part or the whole structure. Finally, the whole building
must be checked against toppling as a rigid body about one edge of the base.
Moments are taken about that edge with the resisting moment of the dead weight
of the structure to be greater than the overturning moment by an acceptable factor
of safety (FS > 3).
6. Drift Limitations: The parameter that measures the lateral stiffness is the drift
index. It is defined as the ratio of the maximum deflection at the top of the building
to the total height of the building. In addition, each floor has an index called the
inter-story drift index which checks for localized excessive deformation. There is
no national code requirement for the drift index, but 1/400 is a traditionally
accepted limit. Different countries use from 0.001 to 0.005 (1/1,000 to as low as
1/200). Lower values are used for hotels and condominiums because the noise and
discomfort at those levels are unacceptable. For conventional structures, the
preferred range is 0.0015 to 0.0030 (in other words, from 1/700 to 1/350)
Deflections must be limited, in order to:1)Prevent second-order P-delta effects due
to gravity loading, precipitating collapse;2) Allow the functioning of non-structural
components, such as elevators and doors;3) Avoid distress in the structure;4)
Prevent excessive cracking and consequent loss of stiffness;5) Avoid any
redistribution of load to non-load-bearing partitions, in-fills, cladding, or glazing;6)
Prevent dynamic motions from causing discomfort to occupants, or affecting
sensitive equipment. In the design process, the stiffness of joints, particularly in

4. precast or prefabricated structures, must be given attention to develop lateral
stiffness of the structure and present progressive failure. Torsional deformations
must not be overlooked, especially due to diurnal thermal drift in steel frames. As
building height increases, the drift index should become lower to keep the top story
deflection to a suitably low level. If excessive, the drift of a structure can be
reduced by: 1) Changing the geometric configuration to alter the mode of lateral
load resistance; 2) Increasing the bending stiffness of the horizontal members; 3)
Adding additional stiffness by the inclusion of stiffer wall or core members; 4)
Achieving stiffer connections, by sloping the exterior columns; 5) In extreme
circumstances, it may be necessary to add dampers, which may be of the passive or
active type.
7. Stiffness: The lateral stiffness is a major consideration in the design of a tall
building. Under the ultimate limit state, the lateral deflections must be limited to
prevent 2nd-order P-delta effects from gravity loading to be large enough to
precipitate collapse. In addition, serviceability requires these deflections not to
affect elevator rails, doors, glass partitions, and prevent dynamic motions to cause
discomfort to the occupants and sensitive equipment. This is one of the major
differences of tall buildings with respect to low-rise buildings.
8. Human Comfort: Buildings subjected to both lateral and torsional deflections
(plus vortex shedding and other usual effects) may induce in their human
occupants from discomfort to acute nausea. These are major factors in the final
design of the building. When a tall structure is subjected to lateral loads, the
resulting oscillatory movements can induce a wide range of responses in the
building’s occupants, ranging from mild discomfort to acute nausea. This may
prove the structure undesirable or un-rentable. There are no codified standards for
comfort criteria. A dynamic analysis is required to determine the response of the
structure in order to determine its adequacy to the comfort criteria.
9. Creep, Shrinkage, and Temperature effects: In very tall buildings, the
cumulative vertical movements due to creep and shrinkage may cause distress in
the structure and induce forces into horizontal elements especially in the upper
regions of the building. During the construction phase, elastic shortening will occur
in the vertical elements of the lower levels due to the additional loads imposed by
the upper floors as they are completed. Cumulative differential movements will
affect the stresses in the subsequent structure, especially in the building that
includes both in-situ and pre-cast components. Buildings subjected to large

5. temperature variations between their external faces and the internal core, and that
are restrained, will experience induced stresses in the members connecting both.
Important factors in determining long-term deformations include:1) Concrete
properties;2) Loading history;3) The age of the concrete at the time of load
application;4) Volume-surface ratio and amount of reinforcement in the members
concerned;5) Achieving a uniformity of stress in the vertical components will
reduce any relative vertical movement due to creep and elastic shortening.
10. Fire: The design considerations for fire preventions and protection, smoke
control, firefighting, and escape are beyond the scope of a book on building
structures .However, since fire appears to be by far the most common extreme
situation that will cause damage in structures, it must be a primary consideration in
the design process. The characteristic feature of a fire such as the temperature and
duration, can be estimated from a knowledge of the important parameters involved,
particularly the quality and nature of combustible material present, the possibility
and extent of ventilation and the geometric and thermal properties of the fire
compartment involved. Once the temperatures at the various surfaces have been
determined, from the gas temperature curve, it is possible to estimate heat flow
through the insulation and structural members. A knowledge of the temperature
gradient across the member, and the degree of restraint afforded by the supports
and surrounding structure, enables the stress in the member to be evaluated .the
mechanical properties of the structural materials ,particularly the elastic modulus
or stiffness and strength ,may deteriorate rapidly as the temperature rises, and the
resistance to loads is greatly reduced .for example the yield stress of mild steel at a
temperature of 700 degree Celsius is only some 10-20 % of its value at room
temperature. Over the same temperature range, the elastic modulus drops by
around 40-50%.the critical temperature at which large deflections or collapse
occurs will thus depend on the materials used, the nature of the structure, and the
loading conditions. The parameters that governs the approach are stochastic in
nature, and the results of any calculation can be given only in probabilistic terms.
The aim should be to achieve a homogeneous design in which the risks due to the
different extreme situations are comparable.
11. The Effect of Foundation Settlement upon the Tall Building: The gravity
and lateral forces on the structure will be transmitted to the earth through the
foundation system. Because of its height, a tall building’s columns may be very

6. heavy. In areas with bedrock, appropriate foundations can be shallow foundations,
drilled shafts, or deep basements. In areas with poor soil conditions, differential
settlements must be avoided. A typical solution is the use of mat (or raft)
foundation, where the weight of soil equals to a significant portion of the gross
building weight. This method is called “partially compensated foundation.
“Overturning moments and resisting moments and shears must be checked. Minor
movements of the foundations are greatly exaggerated by a tall building, leading to
very large inclinations of the tower. If an overall rotational settlement of the entire
foundation occurs, the ensuing lateral deflections will be magnified by the height,
increasing maximum drift and incurring P-delta effects.
12. Soil-Structure Interaction: Soil-structure interaction involves both static and
dynamic behavior. The former is generally treated by simplified models of
subgrade behavior, and finite element methods of analysis are customary. When
considering dynamic effects, both interactions between soil and structure, and any
amplification caused by a coincidence of the natural frequencies of building and
foundation must be included. Seismic forces may develop excessive hydrostatic
pressures, causing liquefaction of the soil. These types of conditions must be
considered and avoided.