Keywords

1 Introduction

People are greatly affected by the fury of the floods. The adverse effects are in the form of direct casualties, spread of waterborne diseases due to lack of proper sanitation, mass evacuation from the place of residence etc. It is reported that catastrophic floods in India between 2013 and 2018 have caused severe casualties in about 14309 villages and 114 districts so much so that about 1187 people have died and more than 16.85 million people were affected (Blom et al. 2012; Haque et al. 2019). The devastating nature of heavy flood events are known to be caused mainly by the high rainfall in the catchment area which finds alternative drainage routes while entering the low gradient plains. Though the regular disaster management approach prefers infrastructural preventive measures like embankments, levees, retention walls etc., it is also important to provide suitable remedial measures as well. While the preventive measures are successful in reducing the disastrous effects of the calamity, it is essential to face the worst cases without much harm by the aid of suitable remedial measures. In this aspect, construction of temporary structures in the vicinity of damage-affected areas is essential to provide quick relief and support for the affected people at least for a short period of time.

Flood shelters are generally constructed in the vicinity of the rivers, but located in safe and elevated grounds which are accessible for emergency services. In many countries, different types of multistoried smart shelters have been introduced as an effective flood management strategy (Kiran et al. 2014; Hussein and Abrahem 2019; Jacob and Althaf 2020). Eastern-Asian countries have implemented various individual home-shed raising schemes in order to rescue the flood refugees. It is a common practice to utilize the primary educational institutions and religious buildings as temporary relief locations. However, such shelters are not capable of providing the required amenities for the huge mass of refugees who have to keep their essential belongings and take care of health by avoiding close contacts (Neilson 2015; Liao et al. 2016). Though thousands of such flood-shelter buildings are in practice even now, there is very little attention to the technical features of these buildings in view of their safety and stability requirements. In addition to this, the variation in geographical and social contexts are mostly missing in the emergency flood relief approach which can be quite indicative in a country like India with huge diversity in demographic and social characteristics.

1.1 Pre-engineered Buildings

The prospects of constructing temporary and (or) portable structures have amassed greatly after the introduction of pre-engineered building (PEB) concept using steel members. The selection of material of construction is one of the preliminary steps while planning for an engineered structural design. Steel is widely chosen as a sustainable construction material for its high strength-weight ratio and also due to its eco-friendliness by reducing the usage of concrete and thereby minimizing the impact of global warming. The essential design and fabrication of PEB are carried out in factories and hence it conserves time as well. Several studies have proclaimed that the construction time is at least 40% less when compared to conventional buildings (Rahman et al. 2015; Saleem and Qureshi 2018; Sivakkumar et al. 2020). Technically, the members are designed in such a way that they are in the form of tapered sections with higher depth (or width) where the force is higher and with minimum depth (or width) where the force is lesser. This reduces the steel requirement to a greater extent. It also contributes to material conservation and greatly reduces the self-weight of the structure. The major expense, however, is associated with the transportation of the fabricated components to the site and their assembling. They are reliable for longer spans that have to be erected without intermediate supports.

Based on the structural analysis using STAAD Pro® software, the pre- engineered structure was found to be 43.24% lighter than ordinary conventional portal frame structure (Jacob and Althaf 2020). They also reported that the secondary members in PEB are much lighter (51.65%) than that of conventional structure. The dynamic load action of PEB buildings using time-history data analysis showed that usage of bracings has greatly reduced the displacements in all three directions (x-axis by 34%, y-axis by 13% and z-axis by 23%). This also has direct influence on reducing the acceleration response to the dynamic loading conditions (Thorat and Patil 2017). Similar results were highlighted by (Saleem and Qureshi 2018) by studying loading responses PEB and conventional frames in terms of reduction in weight and displacements.

1.2 Tactical Urbanism Approach

Tactical urbanism also known DIY (Do It by Yourself) urbanism is a creative approach that uses short-term, low-cost developments which can be scaled up to bring long term developments. The method has been interpreted as an alternative and challenging protocol to the conventional spatial planning methods in order to allocate more utilizable space in a more responsive planning system. There are many perceived obstructions to the direct implementation of this tool in infrastructure development projects, especially in the construction sector where time, man power, materials and money are equally vital in achieving optimum project management goals. The application of Tactical Urbanism in Construction (TUC) is an emerging approach to tackle the most prevalent hurdles in project management by allocating resources in a quicker and cheaper manner without sacrificing their sustainability credibility. In an interesting study, the researchers have suggested to use clamping arrangements on the structural frames for direct insertion of the cladding panels without usage of adhesives or fasteners which would be helpful in conserving time as well as energy (Nielson 2015; Sivakkumar et al. 2020).

Though many researchers are advocating the advantages of PEBs for industrial and public use buildings, their applications in a time-bounded, highly demanding emergency situation has not been addressed so far. The present study aims to provide a strategic solution for easy and safe flood rehabilitation plan with the aid of PEB structures using the principles of tactical urbanism. We propose the suitability of a typical PEB structure based on its structural stability features and ascertain the impacts of TUC based on the envisaged advantages. The proposed solution also highlights the sustainable features with added provisions to ensure the safety and comfort of the people during times of such unavoidable difficulties.

2 Materials and Methods

2.1 Selection of Materials

The typical design of the PEB structure consists of a multistoried housing facility with provisions for easy assembly and erection. The basic materials proposed for construction are listed in Table 1.

Table 1. Details of the selected materials for construction
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2.2 Structural Design Aspects

The proposed flood rehabilitation structure is designed as a truss-roofed, multi-layered steel framed structure with clay panels are walls. The structural design is performed using STAAD Pro® V8i (Series 6) software. The design specifications of the steel framework are provided in Table 2.

Table 2. Specifications of the steel framework
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The various loads applied to the members other than the self-weight of the building is listed in Table 3. The loads considered are self-weight of the structure, rain water load in gutters, wind load (basic wind speed taken as 47 m/s) and seismic loads. For live load on roofs, it is considered as an inaccessible roof. Loads are applied as per IS 875:1987. The sections are chosen as per IS 800:2007. The seismic design is based on IS 1893.1.2002.

Table 3. Types of loads considered on the members (other than self-weight)
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Time history analysis is performed to study the dynamic response of the structure. Ten modes are considered in this study. Damping of 0.05 is considered. Acceleration loading type with integration time of 0.00138 seconds is taken and time versus acceleration is defined accordingly.

2.3 Proposed Strategies for TUC

With a blend of PEB and tactical urbanism concepts, a stable structure is planned to be constructed in short time.

  • It is proposed to make the cladding panels in the construction using clay mixed with a 0.2 µm fraction of CsAgO2 heated to 200 ºC to 550 ºC. The mixture is said to have bactericidal properties and can be of great help in prevention of water borne diseases.

  • Two panels can be inserted into the frames forming a hollow cavity and thus creating a cavity wall arrangement which helps in thermal insulation.

  • Mezzanine floors are chosen as sustainable material with advantage of increased carpet area.

  • The steel is to be coated with mosquito repellent paints as mosquitoes are the major vectors of contagious diseases and their breeding would be high at times of flood.

  • It is a known fact that power supplies would be cut during floods. It affects the livelihood of people. In the proposed rehabilitation structure, it is planned to have simple electrode set-up to use the total dissolved salt (TDS) content of flood water to generate electricity. Though the electricity obtained may not be high, it would be sufficient to light bulbs, charging mobile phones etc. and thus would help people with their basic needs.

  • The structure can be built at a close vicinity of the flood-prone areas on an elevated platform. Though the structure may be ready and unoccupied after construction, hydraulic jacks can be used to elevate the structure at times of need.

  • After the erection of the frames is done, the provision to generate electricity may be given. Then the clay panels are to be inserted into the clamping arrangements provided in the frames.

3 Results and Discussion

3.1 Details of Load Distribution Profile

The skeleton of the structure is modeled in STAAD Pro® and the weight of claddings and other members are added as loads to the members. The various components of the loads are calculated as per the following strategy. The dead loads and live loads are converted to corresponding uniformly distributed loads (UDL) while the wind loads are assigned based wind speed probability distribution profile. The load calculations are as given in Table 4.

Table 4. Loading conditions and calculations
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The important parameters used for wind load are derived from the estimation of design wind speed and wind pressure values. These are basically functions of the topographic features of the load and are assumed for a typical wind-affected scenario (Table 5). The wind load has been calculated separately for the roofs and the walls using the empirical relationship between induced wind angle and the resulting wind pressure. The corresponding wind pressure coefficients were selected based on the perpetuating angle for imparting the loads (0° and 90°) to obtain the distribution of the wind load. The details of the distributed wind loading on the rafter and columns are provided in Table 6. It is clear from the results that the wind loads minimal compared to the dead and live load as expected for the temporary structure.

Table 5. Wind parameters used in this study
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Table 6. Distribution wind loading as UDL on the structural members
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3.2 Structural Stability and Safety Conditions

The selected members were analyzed for their structural stability under different loading conditions in the STAAD Pro® environment and the results were checked for minimum utility ratio (Fig. 1). The optimum sections were thus adopted in such a way that they pass the unity check. Based on the exercise, releases were found to be suitable at column-rafter joints to make the columns act as compression members and not as flexural members.

Fig. 1.
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The 3-D rendered view of the structure in STAAD Pro®.

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It is inferred that the structure as a whole is structurally stable when subjected to both strength and serviceability load combinations to its various members. For about 30 strength combinations and 15 serviceability combinations were applied and the structure was found to be safe under these conditions. As we follow limit state design, it is essential to check both serviceability and strength criteria and that has been done through the load combinations. The structure has been checked for its stability against deflection and bending and the results are quite promising to ensure the stability against deflection and bending responses (Fig. 2). The stress contours of the structure are also showing normal behavior indicating the adaptability of optimized sections using PEB elements.

The sections were optimized in such a way that the utility ratio of the member remains as low as possible. The highest utility ratio of a member in this analysis is found to be 0.986, which is exhibited by a rafter member. Similarly, the lowest utility ratio is exhibited by a gable end rafter member with a value of 0.053. It is invariably found that all the deflection values are within the limits. A typical variation in the profile of shear force and bending moment diagrams of rafters and columns are shown in Fig. 3 administering the maximum possible impacts of extraneous loading conditions. It is observed that all the main columns and rafter have but similar patterns except for the gable end columns and rafters.

Fig. 2.
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Demonstration of structural stability of PEB elements under limit state design, representing (a) optimum sections for safe design; (b) distribution of bending moments at various sections; and (c) distribution of stress contour.

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Fig. 3.
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Representation of typical shear force (SFD) and bending moment diagrams (BMD) for the selected members.

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A typical profile of dynamic loading response has been derived based on the time-history analysis. It is observed that the sectional features are particularly attributed with optimum dimensions of the members so that there is no residual impact for the dynamic loading conditions (Fig. 4). This is further analyzed in terms of the maximum possible extent of the displacements observed in all three directions as a consequence of dynamic loading. The maximum displacements occurred in various directions for various loading cases are listed in Table 7. It can be inferred that the maximum possible displacement in X-direction is attributed to the earthquake load in the X-direction (2.57 cm) and all other possibilities are extremely minute except for wind load in the range of 0.5 cm. However, the maximum positive displacements in the Y-direction (3.32 cm and 3.01 cm) were caused by the wind load with an orientation of (90 + CPI) and (0 + CPI) respectively. Similarly, the highest displacement in the Z-direction was observed to be caused by earthquake loading in the same direction (2.16 cm) while the maximum displacement from the wind load was about 1.70 cm. In addition, the displacement in the opposite direction was found to be highest in the Y-direction due to the dead load (−5.86 cm) and live load (2.52 cm). These results are indicating the necessity of detailed sectional analysis to ensure the structural safety against possible worst-case scenario.

Fig. 4.
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Dynamic response of the structure (sample for representation).

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Table 7. Maximum displacements observed under varying loading conditions
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3.3 Functional Aspects of TUC

As envisaged in the methodology section, the project has administered the practical aspects of TUC in the critical stages of fabrication, construction and erection of the temporary structure. At the outset, it is introduced as a strategic solution to manage the existing constraints in getting the time and workforce to build a temporary shelter at the neck of the bottle moment of emergency situations. It is based on the concept of effective utilization of space with maximum beneficial use in terms of public utility and interior arrangement. The present application has provided sufficient scope for synergistically addressing both the scopes. The method of construction adopted in this study deals with quick assembling of pre-fabricated members at the ease of erecting a tall structure in less time. The specific advantages of implementing TUC in the construction and erection of TUC in selecting PEB for emergency shelter design can be summarized as follows (Table 8).

Table 8. Key functional aspects of TUC in fabrication and erection of PEB based temporary rescue shelters
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The physical architectural view of the structure is modeled in Sketch-up software to give a clear understanding of the design (Figs. 5a and 5b). The entire structure looks attractive with its added features of steps for rising to the higher levels and side shielding for safety and protection.

Fig. 5.
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(a) Front elevation and 5 (b) Architectural view of the PEB-based temporary rescue shelter.

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3.4 Envisaging Sustainability

Addressing the sustainable aspects of the structure as a temporary rescue shelter for flood-affected refugees has wide scope in ensuring their overall safety and quick recovery. On an engineering point of view, there are multiple advantages in terms of environmental and economic aspects by adopting this principle of construction. Use of steel is considered to be the biggest advantage as an eco-friendly construction material with regard to global warming (environmental aspect of sustainability). Due to the high scrap value in the market, the adaptability and recyclability of steel can be considered as the highlight of the proposed model. By incorporating PEB and TUC principles, material costs and labor costs are reduced greatly and thereby contributing to economical aspect of sustainability. In addition, rapid installation with less energy consumption also greatly accounts for sustainability. The cavity wall arrangement helps in thermal insulation and serves as an energy efficient roofing and wall cladding system. Based on the generic metric of sustainability, it is quite possible to demonstrate the long-term benefits of this model as presented in Table 9.

Table 9. Key aspects of sustainability in terms of short and long span of project
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The main intention of the proposal is to serve the needful community at times of natural disaster, thus fulfilling the social aspect of sustainability. A home is a great asset which is a dream for many people in India especially who belong to the lower middle and lower economical section. Many people who live in slums do not have proper shelter and they are the most affected sector in case of natural calamities. During the floods, it is essential for them to stay in a place where they are protected from the dangerous environment. Irrespective of the anticipated communal statuesque, there is a positive socio-cultural interaction developing at the short-term stay with sharing at rescue centers keeping values of the basic amenities of life highest priority. It is to be understood that the structure can safely accommodate fairly a good number of people, say about 20–30 (or 5–6 families) with sufficient space for keeping their essential belonging without damage.

3.5 Recommendations for Emergency Operations

One possible modification to be addressed is in the area of converting this model to a fully portable building. Though we have focused on the foundational aspects of the structure while design, it is nonetheless possible to move the entire structure using hydraulic jacks. As majority of the parts are made up of prefabricated elements with steel and clay, it is quite possible and economic to convert them to portable structures with the concept of PEB frames. The lesser material requirements will lead to decrease in entire weight of the structure, especially when focused on portable type of construction. It is also inferred here that the building must be kept safe from all sorts of natural calamities by proper site investigation prior to construction work and selecting the suitable type of building based on location. The structure has the scope of converting to an IoT (internet of things)-based smart structure by incorporating salient functionalities of communication and automatic control devices. It is an emerging field of aspiration with extreme scope for social implementation in the era of tangible global warming conditions.

4 Conclusions

In this study, a temporary steel-framed structure is designed as a possible rescue shelter for flood rehabilitation using the principle of PEB. The sections are designed as per Indian codes and analyzed using STAAD Pro® environment under various combinations of loads. It was observed that inclusion of bracing could reduce the sway of the compression member while considering the extreme conditions of multiple loading. The maximum deflection under wind loads is approximately 1.70 cm. The proposed construction methodology using TUC was observed to reduce the time (50%) and material (10%) requirements considerably, suggesting as a potential sustainable solution. It is observed that the application of principles of Tactical Urbanism in Construction can help to tackle some of the most prevalent hurdles in emergency relief management by allocating resources in a quicker and cheaper manner without sacrificing their credibility of sustainability.