Structural Flexibility in Buildings- Adaptable Building Design & Construction

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There is a need for structural flexibility in buildings, i.e. design and construction of adaptable buildings which can be modified time to time based on requirements. This articles provides information on how flexibility or adaptability in buildings can be adopted, their types and why it is required. Prologue: The word flexibility has been explained in terms of building quality construction as well as flexibility in structural mechanics. Flexibility property in buildings means they can evolve as per the required performance when any change in already set condition takes place. Structural flexibility of buildings has a role in influencing the service life of existing buildings and the possible life of the building newly constructed.

Stages of Structural flexibility in buildings

Structural flexibility of buildings has following two stages:

1. The design stage: variability in the composition and the use of material;
2. The user stage: flexibility to adjust the composition and the applied building components to the changing demands and/or wishes of the same or varying users while in use.

Why Structural flexibility in buildings or adaptable buildings required?

Considering in structural level, flexibility in the user stage may be translated into possible adaptability of the floors to higher working loads (extreme live load) and the realization of recess for stairwells, lift shafts or pipes and ducts. Urban areas and building have undergone redevelopment when we compare them with past centuries. These were undergoing degeneration before they were met with a redevelopment. Industrial areas with warehouses were transformed into housing or as office spots. As per the past and present record of buildings, many were demolished, but some of them were refurbished and granted a second life of functionality. It is based on the analysis that some of the buildings were more prone to demolishment, but somewhere more suitable for redevelopment. Something that must be noted is that most of the building that had undergone redevelopment was not constructed during their first construction, about the possibilities of remaking it. It was not foreseen. It was not designed to undergo functional changes. It's just a coincidence and favorable factor that made it possible to undergo a refurbishment even though this objective was not foreseen.

Building Service Life Extension

There are certain aspects that would be considered favorable for a second functional working life, which is mentioned below

• Location- Building location quality marks essential criteria that make an engineer to fix his decision in renovating the building.
• Quality of the building and the structural components technically
• Historical value and its architectural quality
• Economy- The aspects of the economy which includes the cost of refurbishment compared against the cost required for demolishing as well as rebuilding and of course the returns in form of profit as service or finance.
• The approval of local urban planning rules and the building regulations
• Building owner or authorities vision.
• Sustainability keeping in mind the environments aspects like air, water pollution, soil conditions etc.

To improve the Performance-based seismic design which primarily aims in taking the performance as the criteria for building design and Integrated Life Cycle Design which involves comparing, balancing and optimizing the decisions at the design stage it is essential to clearly define as well as quantify flexibility more accurately. This clear picture of flexibility would act a tool to evaluate the building structures with our already held building stock in more details manner giving us an opportunity to identify future refurbishment of existing buildings. To acquire an idea on how buildings have to be changed or adapted, a sufficient building model of the one under consideration would let us understand. This enables all the elements that can be changed and all the problem and factors that can be fixed. Certain engineers looked at buildings by distinguishing them to different layers. An adapted list of building layers can be mentioned as follows which includes:

• Scenery
• Space Plan (Walls for partition)
• Access (Lifts, corridors, stairs)
• Service Elements (Pipes, cables building services)
• Envelope (Base, roof, facades)
• Compartments
• Structural elements (Columns, floors, load bearing walls etc.)
• Location

In general, a flexible building structure can be defined a building with the capacity to accommodate in a relatively better with the changes in future. The easily adaptable changes mean the changes happening to the following building layers as mentioned above Scenery or Envelope or Access or structure or its location. Relatively easy employs by the extent of the work necessary for a certain amount of change.

Fig.: Adaptable Building Layers

Structural Flexibility of Buildings Under earthquake

The structural flexibility can be defined as the property of the building structure to accommodate any changes in use by providing sufficient space as well as load-carrying capacity and letting changes in one more of the building layers without the requirement to change the structure itself.

Oscillation of buildings with flexibility

When the ground shakes, the building base can move with the ground movement acting flexible nature. This would cause different building parts to move back and forth. If the structure was a rigid, all the elements would have moved together. A mixture of sinusoidal waves of different frequencies ranging from short to long combines to form an earthquake ground motion. Period of the earthquake wave is the time taken for one complete cycle of motion. What intensity will the earthquake strike the building depend on upon different factors:

• Magnitude of earthquake
• Epicenter distance
• Type of ground the earthquake waves traveled

One way of categorizing buildings over a large city is by their fundamental natural period 'T'. If the ground motion waves have a short period, then short building period would have a larger response. If the ground waves are long period ones, long period buildings would have a larger response.

Structural Flexibility in Buildings - a Key

The most important physical property of earthquake-safe buildings and structures is flexibility. Rigid structures would crumble and collapse during the movement caused by an earthquake. Taller structures are practically more flexible short storey buildings and structures. Hence shorter buildings and structures require greater amounts of reinforcement to withstand the forces of an earthquake. The construction of flexibility gained structures significantly help reduce the amount of damage caused by an earthquake. It is found that wood and steel have greater flexibility than stucco, unreinforced concrete, or masonry. Certain structures are designed to undergo failure in a certain way in the event of an earthquake, which is a performance-based design. Here the failure of the building is pre-planned. Hence planned failings would let protection of the interior spaces, where the occupants or people have chances to be more present. These structures are designed to reduce the amount of rubble and debris that is deposited around the foundation of the structure to keep from damaging nearby buildings. Earthquake reinforcement in structures, constructed with additional strategically placed beams would help in transfer of energy of the sway of the building during a quake to the base of the structure and the surrounding earth. Reinforced beams and trusses can also help prevent warping and collapse of buildings and structures during and after an earthquake. Advances in structural engineering are flourishing with new construction materials, that would enable earthquake-safe buildings and structures to be a reality.