Physical layout and physical security issues must be considered during site planning. Surveillance will be offered in order to prevent terrorist attacks.
By putting up physical barriers and access controls.
Parking near the building is restricted.
Structures that are buried deep underground are safer. Under blast loading, walls with soil cover on the side function well; earth is quite good in reducing the effects of explosions. Buildings with buried roofs have shown to be quite effective in military applications, and they can also be employed in civilian projects with security in mind.
Architectural configuration that affect the design
Shapes that are convex are favoured over those that are concave. Concave shapes feature a number of inner dead ends, known as re-entrant corners, which trap shock wave overpressure; examples are U- or L-shaped structures.
Functional planning by grouping the requirement.
By elevating air intake systems above ground level, they can be protected.
Structural aspects of design for terrorism
The goal is to provide a high level of stiffness as well as strong lateral and vertical strength.
The structural structure of a building has five main aspects that are known to increase the building’s hardness. These characteristics are:
(a) Stiffness and Large Mass: Buildings with a large mass perform well under blast loads; lightweight structures are inappropriate. Because such structures have a lot of inertia, they take a long time to respond to the extreme explosion overpressure. This is advantageous since the explosion overpressure time has gone before the building begins to oscillate. Large mass structures also have a high rigidity, which implies they have less deformations.
(b) Large redundancy: One of the most important factors in the survivability of buildings under blast loading is high redundancy in vertical and lateral load resisting systems with ductile sections linking them. This means that if localised damage occurs in any of the structural elements, load can be re-distributed and the structure can avoid collapsing.
(c) Member Strengths Proportioned as per Capacity Design Concept: Blast loading is a force that is imparted to the structure. As a result, structures are intended to be stronger vertically and laterally than the vertical/horizontal force generated by the blast. Buildings are also developed according to the capacity design idea. This ensures that members do not succumb to brittle shear failure before succumbing to ductile flexural failure. It is critical that the connections allow this without causing damage to themselves. The effectiveness of such a strategy is enhanced.
d) Resistance to Reversed Loading: The reversal of blast overpressure loads, meaning the positive pressure phase followed by the negative pressure phase, is accounted for in the structural design of the principal structural members (resisting vertical and lateral stresses). As a result, structural solutions based on gravity load prestressing and seated connections should be avoided. Roofing systems, in particular, should be bolted or secured down to prevent lift-off in structures due to upward pressure.
(e) Strong Connections: Connections between structural elements must be robust enough to withstand substantial deformations without losing strength, allowing for ductile load redistribution from one vertical and lateral load resisting system to another. Cast-in-situ RC constructions have shown to be effective in a variety of military applications, including military bunkers. Extensive research and testing of cast-in-situ RC structures has shown that it is possible to (a) design ductile RC beams and (b) design columns with high cross-sectional areas that do not buckle when large overpressures create a sudden increase in axial loads.Bearing a load The use of structural configurations must be avoided.
Progressive collapse analysis
(1) Direct blast impacts producing considerable damage to the façade and (2) localised damage owing to attack on individual elements leading to progressive collapse are two design requirements defined by the type of weapon. When a member in the primary load resisting system fails, the force is redistributed to the adjacent members, resulting in gradual collapse. If the neighbouring part is unable to withstand the additional load, the entire structure will fail. The structure continues to deteriorate, and the building eventually collapses. As a result, the failure of a member at the local level leads to the gradual collapse of the structure at the global level, one member at a time. The design for the latter is the more important of the two needs.
As a result, establishing lateral resistance in buildings is primarily concerned with preventing progressive collapse. Regardless of the building’s function, structural system, or level of security, every structure should be constructed to prevent gradual collapse. The first step in ensuring that there are numerous different load routes and a greater number of locations where plastic hinges must be installed before the structure collapses is to ensure redundancy. Members where plastic hinges are expected to form should have ductile details included into them to behave in a ductile manner, and non-ductile members should be constructed according to the capacity design concept to reduce the risk of progressive collapse.
The mechanism to be used to ensure that gradual collapse does not occur is briefly detailed below:
(a) To mimic local damage from an explosion, perform structural analysis of the building by eliminating one critical piece in the load path, such as a column, load-bearing wall, or beam. The analysis method can be both linear and nonlinear, and it can be both static and dynamic.
(b) Determine whether the remaining structure’s available load path can withstand the load. If it is possible, the practise is repeated by deleting another critical load route piece. Otherwise, the structure will be exposed.
(c) A structure is said to meet the progressive collapse criteria if it can resist loading in all feasible scenarios of removing an important member in the load path one at a time.
Design Methods
In the literature (ASCE 7, 2002), three strategies for structural design of buildings to limit damage due to progressive collapse when blast loading initiates collapse have been found. These are the following:
(a) Indirect Method: Prescriptive standards are followed in order to increase structural integrity. These standards cover everything from choosing a structural system to locating the primary lateral load resisting systems, proportioning members, and specifying them for ductility.
(b) Alternate-Load-Route Method: The structure is designed to withstand the forces imposed by gravity and wind loads while accounting for the loss of one important load-bearing part in the load path. This strategy is only applicable to loads other than blast loads. Identifying the crucial member-loss scenarios that have the worst effect may necessitate the assistance of design specialists specialising in blast effect design;
(c) Specific Local-Resistance Method: This is the most thorough method, as it takes into account both blast loading and the structure’s nonlinear response. As a result, the approach of analysis encompasses both nonlinear and dynamic structural response. In this analysis, the location of blast loading is critical. Typically, blasts occur in the lower levels, with the weapon either under the building or at a safe distance from the façade.
Buildings serve a variety of purposes, including providing living space, manufacturing, utility generation and distribution, commercial business activities, transportation hubs, and leisure and recreation facilities.
Buildings are designed with the occupants’ comfort and safety in mind, as well as the most cost-effective use of space, the efficiency of corporate processes, record storage, and business support systems such complicated information technology networks and computers. They’re becoming more and more adaptive in their use, resulting in vast adaptable internal areas and non-structural facades.
Consider the inherent flaws of structures as a starting point. The type of construction, articl, has a big impact on a building’s ability to withstand an explosive attack. A structure with a solid, well-tied frame will be sturdy in this regard, whereas a structure with stone walls and no frame can easily collapse. A building with uncontrolled entry will make it easier for a terrorist device to be delivered inside. Terrorists will employ pedestrian and vehicle access, as well as the access channels for the building’s numerous utilities. The building’s location in relation to its surroundings will also play a role, as key security measures are sometimes impossible to implement due to the limits of a congested environment.
Terrorist acts may appear to be random and unpredictable, but research into the terrorist’s psychology and motivations can provide vital insights. Terrorists are looking for a way to generate publicity in order to impose pressure on, or even overthrow, the current government. Terrorists, it is commonly argued, do not seek to inflict casualties in and of themselves, but rather the impact caused by casualties. To attain those goals, three broad strategies are employed. Terrorists want to demonstrate that a government or organisation cannot safeguard its citizens by killing or injuring them. Second, terrorists want to demonstrate that a government or an organisation can no longer function by causing disruption. Terrorists, third, cause or threaten unacceptably high economic losses.
Also Check
REGULATION FOR PROJECTIONS FROM BUILDINGS