Engineering and construction: Exogenous and Structural Constraints - Essay Example

Engineering and construction: Exogenous and Structural Constraints After the various kinds of knowledge discussed in the previous segments in an appropriate format, it is possible for someone to reason from such knowledge to obtain design answers for a given problem. The structure we put forth for tackling such a task comprises of formulating, propagating and satisfying constraints. Thus, constraints may be devised on the basis of information regarding the context of the project such as location and project-independent knowledge such as overall structural engineering rules .Therefore as section 1.3 demonstrates ,provided the fact that a building(project-specific information) was the facility to be designed, we can devise the constraint that one should gather distributed vertical weights. Providing a structural element Floor Plate will take care of the constraint; nevertheless, through the propagation process, someone can formulate some extra constraints. For instance, someone now requires some structural component(s) that can gather the weight from the floor plate and effectively transmit it to the ground. Thus, the constraints that may be devised may occur from structural deliberations or exogenous such as constructibility, mechanical and architectural considerations. Thus, constraints emanating from various domains might interact with one another, hence building mutual constraints. For instance, considering a high-rise office building floor system, in a characteristic floor system, architectural and mechanical components (ceiling and ductwork) are also present together with structural components such as floor slab and girder. Therefore, mechanical depth, ceiling height and structural depth form a mutually constrained combination such that when considered in together with the needed floor-to-ceiling height, they must not contravene the controls on the tolerable floor-to-floor height. The result of such an association is that disparity in the constraints of some domain may affect the choices in other domain(s).Hence if the mechanical ducts depth is enlarged, one may be forced to minimize the depth of girders or, otherwise, if the ducts were primarily beneath the girders, they might now have to be passed via the girders. The 2 top-level classes of constraints, specifically exogenous constraints and structural constraints can be further decomposed according to the classification put forward by Luth[13].Thus the subclasses are illustrated diagrammatically as indicated in fig 1.1 and are explained in the two subsections that follow. 1.8.1 Structural Constraints Structural constraints comprise of behavior, function, geometry, performance, reliability and product constraints. Constraints emanating from other subsystems (exogenous constraints) should be changed into one of these forms of constraints before their effect on the structure can be taken into consideration. Corresponding to the principal purpose of the structure as discussed in section 1.1, function constraints refer to the weights as well as their locations in relation to the ground. The weights can be explained in terms of forces having a direction, a magnitude as well as a location in space. Some components of the structure might also perform an architectural role, for instance, a slab, besides carrying out the structural role of bearing weights, might also be a functional object floor from the perspective of the architect. In instances such as these, there might be constraints on the physical object emanating from its role in another domain. Thus behavior constraints are obtained from the behavioral component of the knowledge in Behavior and Performance Knowledge element. They are helpful in establishing the reaction of the structure while it’s carrying out its role of bearing weight. The behavior is determined by such primary principles as Hooke’s law as well as superposition principle. Thus, behavior constraints are entirely “difficult” constraints and cannot be loosened up under any situations. Performance constraints are on the basis of knowledge related to requirements together with other performance principle in the Behavior and Performance Knowledge element. Limits are placed on the behavior values exhibited by the structure when subjected to weights and therefore improve serviceability and safety of the facility. When performance constraints are not adhered to, one might have to change one or more of (1) member material, (b) structure topology as well as geometric features, to change behavior in such a manner that the appropriate performance constraints are fulfilled. Furthermore, performance constraints may be divided into safety and serviceability constraints. Safety constraints restricts the internal stresses (as regards the design of working stress) in the member, or defines a relationship between the member capacity and the member force demand for that kind of force (as regards the resistance and weight factor design for steel or strength design for concrete). On the other hand serviceability constraints restrict amongst other things, the cracking, vibrations and deflection of a structure or member. Geometry constraints describe the spatial and location relationships of the structural components. Product knowledge in several cases may also be converted into geometry constraints. Constraints emanating in other domains are frequently a source of geometry constraints on the structural system. Some examples of geometry constraints that come about because of consideration constructibility include concrete beams that should be spaced at a defined interval in order to contain a specified arrangement of types, spacing boundaries on steel beams which are a function of the fabricating connections costs and restrictions on member sizes on the basis of shipping needs and crane capability. Product constraints typify the available spectrum of choices pertaining particular members and materials. They are characteristically a consequence of alteration of the knowledge enclosed in Product Knowledge component. Systems Knowledge and Structural Elements might also be a source of product constraints; for instance, reinforced steel and concrete might be the only functional materials for a framed tube. The user may additionally also impose definite constraints; for instance, though both concrete and steel tubes might be possible, the user might want the choice of steel tubes only to be explored. Several constraints in this class may also begin within the construction domain .A good example of a constructibility constraint which changes into a product constraint within the structural design domain may be the concrete strengths that can be formed in the region within the location of the facility. Reliability constraints facilitate exercising of engineering knowledge and/or decision to explain for the likelihood that the behavior of a substitute will be satisfactory. Redundancy, which is a feature of the structure associated to its function, is an illustration of a qualitative gage of the dependability of a structure. The structure is “non-redundant” if there is only one path for the weights to follow. In cases where there are numerous load paths such that when there is failure in one component the weight can still be effectively transmitted via an alternative way, the structure is known as “redundant.” Generally, redundant structures are regarded as being more dependable. Reliability of different structural systems is indirectly regarded in the technique of establishing the seismic design weights. Some features of reliability are indirect in the resistance and weight factors utilized in the limit state design of concrete and steel structures. For the better part, though, techniques of directly incorporating reliability issues during structural design have not been made official. 1.8.2 Exogenous Constraints Exogenous constraints may be described as those constraints that are pertinent to the structural design, but which emanate from a domain that is out of the range of structural engineering. These constraints may originate from constructability, MEP, owner, architectural considerations. Because buildings have numerous other critical considerations apart from the structural system, exogenous constraints have a particularly pronounced effect in the case of buildings. Not every kind of exogenous constraints explained below may be available for all forms of structures; for instance, MEP constraints may not be appropriate for bridge structures; nevertheless, they will be suitable for power plants. Architectural constraints come about due to the interconnection between structural design and architectural design of a given facility. The geometrical context for the structural system in the facility is defined by the architectural form. The aesthetic appearance might have an impact on the geometric lineup of the components in the structure for purposes of visual effect. Moreover, individual aspects of the architecture also lead to considerable constraints on the structure. For instance, column placement might be excluded in the indoor stadium’s central arena. MEP constraints are extremely significant in the case of high-rise buildings as well as several other kinds of structure. Every electrical, plumbing, and mechanical subsystems can be subdivided into key subsystems whose roles can be categorized as distribution, origination as well as delivery. In addition, the subsystems are a compilation of elements with physical aspects such as weight and size. Because of their size features, the MEP elements compete with architectural and structural system elements for a split of the limited space defined by the building envelope (roof, foundation, exterior walls). Therefore one kind of interaction is geometric. It should be noted that the weight features of the subsystem elements become function constraints on the structure, hence presenting a second kind of interaction. The third form of interaction takes place due to the behavioral features of the subsystems within the context of the building utilization. As an example, vibration and noise coming from equipment operation may need to be removed from spaces that are adjacent. Owner constraints normally involve factors affecting the apparent facility value, expenses involved in facility management or the program for facility construction. Amongst these are constraints touching on floor vibration limits, designation of specific regions as high load intensity regions as well as the cost involved in structure modification to accommodate changing needs. The owner might also have definite schedule requirements on the basis of the facility needs. Thus in such a case as this, an extra constraint on the conceptual design is that it ought to be constructible in the allowable time frame. Constructibility constraints come about due to construction activities considerations. Some sources of constructibility include equipment capabilities, formwork considerations, material availability etc. Furthermore, due to variations in labor costs, available materials, available technology together with variations in the preferences of the owner and designer communities, specific structural systems are preferred in some parts of the nation. This favoritism is normally obvious in the costs that are related with the systems and must be considered at the conceptual design phase. Several times constructibility decisions are also inherent in the problem-solving approach. For instance, a new type is required in case of concrete for each difference in the size and shape of a structural element. In regard of such constructibility consideration, while coming up with solutions someone may endeavor for uniformity in the size and shape of structural members. Read More