In order to establish the integrity of multi-storey buildings, three key design philosophies are used: permissible stress; load factor; and limit state approach. The approaches are important as they facilitate the attainment of serviceability, economy, safety and functionality conditions. The approaches are elaborated further below.
Permissible stress method
Bhavikatti (2010) notes that the permissible stress also known as the Working Stress Method (WSM), is the oldest systematic analytical method developed. The author further adds that the method, which was introduced in the early 20th century, was primarily based on linear elastic theory. As such, it would be used in the design of timber and steel structures as well as reinforced steel.
Bandyopadhyay (2008) further notes that the main assumption with the approach is that, structural material behaviour is restricted within a linear elastic region and as such, its safety is ensured by restricting the stresses being imposed on its members by working loads. As a result, the method would enable structural engineers to ensure that the stresses imposed on structures, as a result of service load, did not exceed the elastic limit.
In essence, the permissible stress method entails an approach where the ultimate strengths of construction materials are divided by a factor of safety in order to ensure design stresses produced are within the elastic range (Bhavikatti, 2010). The author adds that the permissible strength is kept as a fraction of the yield stress, with the ratio of the yield stress to the permissible strength being referred to as a factor of safety. The formula is provided below.
permissible stress =
Advantages
First, the method is simple to use. Second, it is reasonably reliable as it is the alternative approach to be used where the preferred limit state approach is unavailable. Bandyopadhyay (2008) cites that the method is still in use in the construction of chimneys and special structures such as water tanks in India.
Third, serviceability requirements are satisfied automatically given that the working stresses are relatively low. Fourth, since it was the earliest design philosophy devised, there are numerous literature sources detailing the philosophy in addition to a large number of engineers who are used to the method.
Limitations
Despite the simplicity and reliability of the method, it is however plagued by several challenges. First, it gives the assumption that the factor of safety multiplied by working load equals the failure load which is false. Bhavikatti (2010) argues that the failure load is higher since a material can resist the load after the appearance of yields at a fiber. As such, the redistribution of moments leads to additional load carrying capacity.
Second, it assumes that concrete is elastic which is also false as concrete behaves in an inelastic manner. Third, it does not make provision for uncertainties associated with the estimation of loads and as such, does not use any factor of safety in respect to loads. Fourth, it does not account for creep or shrinkage which are time dependent and elastic in nature. Finally, the method results in uneconomical sections and fails to highlight conditions arising during collapse.
Load factor method
According to Pillai " Menon (2011), the load factor method, also known as the Ultimate Load Method (ULM) or Ultimate Strength Method, arose out of a growing concern of the limitations associated with the WSM method in designing reinforced concrete structures. Bhavikatti (2010) notes that the latter was particularly limited in assessing the actual load carrying capacity. Pillai " Menon (2011) further add that the load factor method also emerged following increased understanding of the behaviour of reinforced concrete at ultimate loads.
With the method, calculations utilize the ultimate strength of the materials. As such, the ultimate load is used as the design load. Load factors are multiplied by the working loads in order to obtain ultimate loads. As such, the load factors give the exact margins of safety in terms of load. Additionally, the method considers the real stress-strain curve of concrete and steel and as a result, considers the plastic behaviour of the materials.
Advantages
First, unlike the WSM approach, the load factor method takes into account the non-linear behaviour of concrete. As such, it is more realistic. Second, the method gives the exact margin of safety for the load unlike the working stress method which does not provide specific details about the collapse. Third, it is more economical compared to WSM as it results in thinner sections that require less reinforcement either through thinner steel beams or concrete columns. Fourth, the method takes into account the redistribution of internal forces and finally, it allows varied selection of factors.
Limitations
Despite its economic advantage in generating thinner sections, the thin sections however lead to excessive deformations and cracking thereby making the structures unserviceable. Second, the method does not employ any factors of safety in material stresses. As such, this implies that the method does not consider the variability of materials and as such, cannot be used to calculate the deflections or cracking at workloads.
Limit state approach
By definition, a limit state describes a building’s condition where it no longer meets its defined criteria of design (Punmia, Jain " Jain, 2007). As such, it refers to its conditions of potential failure where failure describes a state that makes the design infeasible. The authors further note that the limit state approach arose given the constraints of the load factor method particularly in regards to serviceability and strength of material. Consequently, Punmia, Jain " Jain (2007) argue that the limit state method is the most preferred design philosophy as it considers both requirements of serviceability and the ultimate strength of the structure.
Bhavikatti (2010) further notes that the method overcomes the constraints fronted by the two earlier approaches given that it divides the ultimate strengths of the materials by partial factors of safety and multiplies working loads by additional partial factors of safety. The author adds that two basic limit states exist: Serviceability Limit States (SLS) and Ultimate Limit States (ULS).
The Serviceability Limit States (SLS) in essence, represents a level of stress within a building below which there is high expectation that the building can continue to be used as it was originally designed without the requirement for any repairs. Bhavikatti (2010) highlights two important serviceability limit states, deflection and cracking. The author notes that with the former, deflections should not adversely affect the efficiency of any part of the building’s structure while with the latter, damage from cracking must not affect the appearance of the structure.
The Ultimate Limit States (ULS) on the other hand, requires that structures should be able to withstand the loads that it was originally designed to handle, with an adequate factor of safety. Additionally, Punmia, Jain " Jain (2007) add that the possibility of buckling ought to be taken into account as well.
Advantages
First, the method combines both aspects of serviceability and safety thereby overcoming the challenges associated with the earlier approaches. Second, it is more economical than the two earlier approaches. Third, it takes into account uncertainty both in loading and material strength rather than a single factor of safety (WSM) or load (ULM).
Limitations
Duggal (2014) notes that the only disadvantage associated with the method is that there is an increased likelihood of error in the design given its increased complexity which might outweigh the benefits of a better theoretical method.
1.2 Structural frames feasibility analysis
In order to develop the office park complex, the feasibility analysis of available structural frames is significant. The three types analyzed include steel frames, insitu concrete, and composite construction.
Steel frames
Li " Li (2007) note that steel is widely used in the construction of structural frames owing to its inherent properties. First, the authors note that mild steel, a variant of steel used in construction, is immensely strong. For instance, a steel bar that is only 25mm in diameter is able to withstand weights of up-to 20 tons without breaking. Secondly, steel is flexible and as such, can easily bend without breaking. Consequently, in the event of earthquakes, steel buildings are able to flex onto one side.
Thirdly, Li " Li (2007) note that steel is plastic or ductile in nature thereby being able to bend out of shape when subjected to great force. As such, inhabitants dwelling in steel framed structures are able to identify any areas with deformity in advance. Finally, steel structures do not easily collapse while at the same time, wrapping them with non combustible material enables them to withstand high temperatures.
Based on its inherent characteristics, steel is widely used in diverse areas ranging from high rise and industrial buildings to warehouse and residential buildings. In the different structures, it is preferred as the material of choice following its strength, low weight, and fast speed of construction. Ramaswamy, Eekhout " Suresh (2007) further note that in steel building, also referred to as steel fabrication, three variants of steel based construction can be adopted.
First, is conventional steel fabrication where steel fabricators cut steel members to their correct lengths and weld them together in the final structure. The fabrication can either be done at the construction site or at the workshop. In the former’s case, it is however labour intensive. Second, is bolt steel construction where steel fabricators produce finished steel products that are shipped to the required site. Finally, light gauge steel fabrication describes a form of residential construction where sheets of steel, bent in form of c or z sections, are used in residential construction.
Advantages
A major advantage of steel construction is its durability. Adopting steel in building structural frames saves building owners numerous costs as fees for maintenance fees, repair and replacements are minimal over the lifetime of the buildings. Second, building with steel is economical as it facilitates faster construction times. A reason for the observation arises from the fact that pre-engineered steel parts are shipped to construction sites ready for building thereby eliminating the need to measure and cut on site (Li " Li, 2007).
Third, steel is environmentally friendly in construction since it is easily recycled. As such, it eliminates costs of developing landfills to handle construction waste. Fourth, steel is versatile in nature and can be easily modeled into any shape. As such, it makes it an attractive alternative in residential construction where other materials are not suitable. Additionally, its versatility enables it to be fabricated easily into different sizes that are appropriate for construction.
Fifth, it is a sustainable construction material as it is resistant to fire, pests, insects and water effects. As such, it hinders the spread of fire in the event it occurs, offers immunity to the detrimental effects of burrowing insects, and is immune to wet weather conditions.
Limitations
Despite its numerous advantages, using steel as the material for structural construction is associated with several challenges. First, costs of construction with the material are relatively high in comparison to alternatives such as wood. Ramaswamy, Eekhout " Suresh (2007) note that costs increase due to the fact that assembling the different attachments consumes a lot of time compared to its alternatives using nails.
Secondly, steel is a good thermal conductor. As a result, buildings developed using steel fabrication are not good at retaining heat. Consequently, this implies that there is a need for additional insulation measures in steel fabricated buildings which increases costs. Thirdly, working with steel on site is not as flexible as using other materials such as wood. With the latter, it is easy to adjust them on site while with steel, materials are shipped ready to be erected at the construction site. The observation, while is an advantage, lowers the flexibility of working with it in construction.
Thirdly, steel frame structures require additional materials in order for a building to be complete. As such, the argument advanced against its use is the aspect that steel never works on its own. Often, there is the requirement for insulation, wooden support structures, sheathing, drywalls, among others.
In-situ concrete
According to Illingworth (2008), in-situ concrete describes concrete which is cast in its final location, that is, on site. The author notes that it was the primary construction method in the early 20th century before technology advancement made it possible to cast concrete in separate locations from where they were finally deployed, that is, precast concrete. Illingworth (2008) further adds that the former is widely employed in traditional concrete floors and strip foundations unlike the latter which is employed in precast walls, precast stairs, concrete masonry units among others.
Advantages
The major advantage with in-situ concrete is its ability to adapt to any building shape. Secondly, given its traditional application methodology, there is no need for highly complex machines such as cranes as is required with precast concrete. Thirdly, the method is suitable for two way structural systems as it is easy to use. Fourth, it saves the builders the agony of fixing complicated joints as is the case with precast concrete. With in-situ concrete, it is possible to adapt to post tensioning.
Finally, since builders are able to control all steps involved with in-situ construction, from batching, to mixing and placing the concrete, the method is argued to be more flexible that precast concrete.
Limitations
A major disadvantage of the method is that it consumes a lot of time. A reason for the observation arises from the fact that the method is comprised of an array of different procedures. For instance, the builder has to prepare for batching, mixing and placement in addition to curing the concrete. Second, before loading concrete, there is a requirement for curing. Thirdly, the requirement for curing implies that harsh climatic conditions create problems for the construction. Fourth, there lacks a surety on the quality of structures developed as workmanship and skillsets vary among different builders.
Composite construction
Johnson (2007) notes that composite construction describes that which is comprised of structural members that are made up of two or more different elements. The author notes that in most cases, steel and concrete are combined together in the construction. Peng (2014) further adds that they style of construction is widely applied in the non-residential sector due to the strength and stiffness that is easily achieved with minimum use of materials. The author notes that while concrete is good in compression, steel offers high tension ability. Consequently, bringing the two materials together as in the case with composite construction, results in a design that is both lightweight and highly efficient.
Advantages
The major advantages arising from the use of composite construction materials pertain to increased value, performance and speeds of construction. To begin with, speeds of construction increase with the use of composite materials since more than one element is used in the construction. Secondly, improved performance is seen to arise through the lightweight nature of the composite material. In essence, composite structures are made up of steel and concrete. Upon combining the two materials, the overall weight of steel in the resulting composite material reduces significantly thereby necessitating shallower beam depths. The implication of such reduction in depth is that it leads to lower costs.
Thirdly, composite floors are stiffer and offer higher strength capabilities following the different advantages brought by the two materials.
Limitations
While composite construction is associated with minimal disadvantages, limitations however arise in terms of costs of construction and the manpower required to undertake the work. On the one hand, combining the two materials requires skilled manpower while on the other, costs of the materials are high. As a result, the overall project costs increase substantially.
1.3 Structural frames material specification
Given that the building under construction is a multi storey complex for rental purposes, composite construction is advocated. Reasons for its selection over steel structural frames and in-situ construction include the need to build the complex over a short duration of time in addition to guaranteeing high performance of the overall structure once completed. By combining both steel and concrete, the overall quality of the building will be significantly higher owing to the advantages arising from the two materials.
A façade system describes the interface between a building’s external and internal environment (Moe, 2010).The author further notes that façade systems are made up of structural elements that avail diverse properties such as wind, weather and fire resistance. In addition, Moe (2010) notes that the façade system used in a given building is highly influenced by factors such as the type of building, its overall scale, and local planning requirements.
In the current scenario, the rental multi-storey complex is to be developed in the docks of the Associated British Ports. As such, the façade system proposed should serve three major functions. First, given the nature of the weather at the docks, the façade should facilitate weather tightness. As such, aspects such as the entry of water and air permeability ought to be taken into consideration.
Second, the façade system should be able to provide some form of thermal insulation in order to ensure the occupants of the building do not suffer adversely from the negative effects of the weather. Thirdly, it should also be able to control aspects such as solar gain and ultraviolet radiation. Finally, an aesthetic appeal is also anticipated to be attained through the façade system developed.
Based on the given reasons, it is recommended that a light steel walling structure should be used to implement the façade system. Additionally, diverse façade materials should be attached to the system such as insulated render, terracotta tiles and metallic panels. Further, glass material should be adopted for the windows with projections of solar balconies being recommended to improve both the aesthetical appeal of the building and ensure the occupants are well protected from adverse weather.
The materials selected for the façade, namely, steel walling, glass windows, terracotta tiles and insulated render are appropriate for the building structure given the anticipated weather conditions at the docks. The different materials not only serve critical functions such as influencing day lighting quality, thermal comfort and energy related performance, they as well add to the aesthetics of the multi-storey complex.
In summary, given that the multi-storey rental complex is to be developed at the docks, there is need for the project managers and structural engineers to ensure the façade system so developed is appropriate for the nature of environment anticipated in the given area. Three alternative façade systems are as a result recommended.
First, are the light steel infill wall façade systems. Benefits associated with such systems include rapid construction rates, less material requirement at the actual site, suitability to different types of cladding material, and light-weightiness. A second alternative is the use of curtain walling where structural frames directly support lightweight metallic cladding or glazed cladding systems. The façade system ensures the attainment of the necessary functions, namely, weather tightness, thermal lighting, and day lighting control.
Finally, is a steel façade system comprised of light infill steel walls. Despite such a system guaranteeing both thermal and acoustic insulation and general fire resistance given the incombustible nature of steel, the façade system is however more expensive to implement. Aesthetically, different textures and colors are however possible. It is thus important that the type of façade system to be adopted in building the multi-storey complex adheres to the set requirements in addition to remaining under budget.
2.1 Systems providing flexible spatial planning
Several spatial systems can be adopted in providing flexibility in the multi-storey building in order to satisfy the variations that the lease clients require to be undertaken before they can take the offices. First, is the land use aspect. Spatial planning advocates for the use of land in a manner that allows sustainability by taking into consideration the different social, economic and environmental impacts.
With the building, land use comes into play in that it restrains expansion of the structure beyond unacceptable areas. Additionally, it facilitates the expansion of the building to incorporate any requirements that may be required by the tenants. As a result, tenants are able to request for the addition of more resources through the available spatial plans.
Advantages of land use spatial techniques include: availing necessary land to allow for additional expansion uses; providing sustainability through the consideration of economic, social and environmental concerns; and reducing costs of daily operation and maintenance for the given landscape. Disadvantages however include the increased costs of implementing the techniques and the fact that the exercise is time consuming.
The second spatial technique pertains to environmental impact. In the technique, the tenants are able to request for variations that reduce their carbon footprint as they lease the building. For instance, they may request for additional aspects that help minimize climate change impact such as renewable energy and energy efficient appliances. The direct advantage of the technique is that it results in improved biodiversity which translates to improved morale of the workers occupying the building.
The disadvantage however regards to the high costs involved in implementing the solution. For instance, procuring energy efficient appliances might end up consuming too much costs. Additionally, adopting alternative energy sources might introduce a challenge given that the building constructors might not have availed any provisions for the same in the building’s blueprints.
The third technique pertains to energy use and the control of noise. With the technique, emphasis is laid upon reducing noise levels within the building’s habitable space in addition to reducing energy use. As a result, the spatial technique advocates for appropriate ambient lighting to replace daylight in addition to accent lighting for the atmosphere, and task lighting to facilitate working. In scenarios where tenants request for more lighting, the spatial plans guide the given directives. Similarly, where requests for noise reduction are made, the plan gives different recommendations.
The advantage with the technique is that it avails appropriate lighting requirements to facilitate working and habitation for the occupants in addition to providing a quiet and serene work atmosphere free of noise. The disadvantage however, pertains to costs of implementing the given services within the established building structure. Similarly, a challenge might exist in introducing the given variations into an already implemented design.
2.2 Influence of the internal system layout
The building’s service engineer has a reason to worry about the impact of spatial planning techniques on the established building services. A particular concern arises with the integration of the building services within the internal system layout. A reason for this stems from the fact that some variants requested by the tenants might necessitate radical changes in the internal system layout thereby making it difficult to implement the solutions. For instance, in order to reduce carbon footprint, tenants might request for renewable sources of energy and in effect necessitate changes in how the internal layout of the building is configured.
However, in order to alleviate the challenge, the internal system layout adopted for the building should be flexible in a manner that allows integration of any variations. For instance, sources of power should not be restricted based on the building’s layout but instead, should be flexible enough to easily move from one location to the next within the building’s layout. Similarly, the design of the layout should not dictate how the building will be used eventually.
Secondly, the building’s engineer should ensure the building has adequate provisions to cater for any additional variations requested by the tenants of the building. For instance, there ought to be provisions for renewable sources of energy in addition to insulation against any noise and temperature increase.
On the other hand, the engineer should keep in mind that there might be difficulty in aligning some of the layout’s aspects to allow sustainability. In such instances, requests by the tenants would have to be turned down in order to avoid introducing irrational changes in the current building’s structure.
3.1 Advantages and disadvantages of buildability
According to Illingworth (2008), buildability describes the degree to which, a building’s design facilitates construction ease, subject to the overall requirements for the completed building. As such, the author argues that buildability leads to cost savings for the designer, client and the builders given that the concept acknowledges the problems of the assembly process in attaining the desired result both safely and at the least cost to clients.
Hyde (1995) further adds that with the concept, the building’s designer is well aware of the method adopted in the construction beforehand. The author notes that the opposite of the approach is loosely described as the artistic method where the designer creates the design to be built with little consideration on how the actual building should be constructed. Consequently, based on the definitions, it is understood that buildability eases the construction process. Additionally, it is associated with several advantages and disadvantages in terms of economy, health and safety, efficiency, economy and quality. These are further elaborated below.
Health and Safety
Buildability introduces several advantages in regard to health and safety. First, it results in the development of a non toxic, sustainable environment that guarantees long term health. As the engineers factor in all possible hazards that would result from the construction, health and safety aspects are improved significantly. Second, buildability emphasizes on equity and human rights by providing a guarantee of safety standards in the environment.
Efficiency
In terms of efficiency, buildability results in transparency and accountability on the part of the engineers. As a result, they are more conscious of the decisions they make and implement. Secondly, the efficiency of designers and builders improves as they focus on only the constructible aspects of a building.
Economy
Economically, giving careful thought to the process of construction leads to minimal costs as wasteful elements are eliminated. The designer, client and builders all save costs as they focus on only what is required for a given construction project. Additionally, as it enhances the health and safety aspects in a construction site, losses arising from unexpected incidences are minimized.
Quality
Buildability results in improved quality of construction as there are less variations in orders, minimized operation troubles, and improved satisfaction by the clients. In essence, as less problems are spent in delivering a given construction project, the overall quality of the structure and project improves significantly.
4.1 Features of a sustainable construction strategy
According to Pearce " Ahn (2013), the concept of sustainability in the construction sector has received significant attention, over the years, owing to its impact on human health and the ecological environment. Consequently, a need arises to develop a sustainable construction strategy in order to support successful outcomes.
The authors further note that an effective construction strategy encompasses three key aspects: economic, social and environmental. In the different instances, the strategy has an influence on planning, design, construction and the finished product resulting from the construction project.
Economic
A sustainable strategy influences planning in that, it helps link different goals, both nationally and at regional levels, to a sustainable context. The implication of such an action is that it enhances the economy through two main ways. First, planning helps prioritize areas that require investment easily. The local government is able to encourage both private and public investment through plans. Secondly, such a strategy has an influence on the objective setting process thereby influencing the economic viability of the given areas and in effect, encourage sustainable development.
In terms of design, the strategy has an influence on the development of different levels of flexibility and functionality, appraisal and costing, and the design for accessibility. As the strategy directs how the different aspects are to be undertaken, an improvement in the economic status improves significantly. For instance, in terms of the flexibility and functionality, a sustainable strategy advocates for good design to reduce maintenance and daily operational costs. In effect, this improves the client satisfaction and quality of structures resulting from the given designs.
Additionally, as the strategy influences aspects of appraisal and costing, this has a direct influence on the decisions made regarding the expected building solutions. Consequently, this has an influence on the expectations of building owners and users. Finally, in terms of accessibility, an effective construction strategy influences the accessibility aspects of buildings, with major impact on developing accessible and safe building structures. For instance, the strategy directs issues pertaining to safety, circulation and signage which has a significant influence on the lives of individuals inhabiting the given structures.
In terms of construction, effective construction strategies advocate for the use of Key Performance Indicators (KPIs) and the maximization of opportunities for local businesses, training and labour. By introducing KPIs, the strategy implements innovative procedures to evaluate the performance of organizations across the industry. As a result, it helps streamline performance thereby improving the economic aspects of such organizations. Similarly, by maximizing opportunities for local construction businesses, the strategy aims to enhance the sustainability aspects of the construction industry.
Finally, in terms of the finished product, sustainable construction strategies have an impact on how the final developed product is maintained in terms of its operations. As such, the strategy advocates for careful management
