Performance and protection of pre-engineered buildings subjected to blast and earthquake excitations

A pre-engineered building (PEB) refers to a building which is pre-designed at a factory using some simulation and modelling software as per the specifications, codes and the loads that act on the structure before the production of the building components and then finally assembled at site thereby reducing the completion time. In the current study, a case study of an existing PEB structure subjected to wind analysis has been investigated. The main objective of the present study is to evaluate the retrofitting ability of passive control dampers installed in the pre-engineered industrial building subjected to earthquake and blast phenomenon. The study investigates the effectiveness of vibration control techniques in the form of passive dampers in improving the performance of PEB structure subjected to blast and earthquake using fluid viscous dampers. The study also discusses the impact of different damper placement techniques on the structural performance of PEB structure subjected to blast and earthquake loading. Primarily three damper placement techniques are incorporated in the present study, namely single diagonal, V-shaped damper, and inverted V-shaped damper. The study also evaluates the optimum fluid damper properties, namely damping coefficient and damping exponent, in mitigating the blast and earthquake responses of the selected industrial building. The structural performance of PEB structure has been studied using finite element tool considering the nonlinear analysis and comparing the structural responses for with and without damper conditions. The V-shaped and inverted V-shaped damper placement techniques are the most effective approach in resisting the damaging effects against blasts and earthquakes for the selected PEB structure in comparison with the conventional diagonal braced dampers. The study reports reductions in structural displacements and brace forces in the range of 54–68% and 70–90%, respectively, when installed with V-shaped fluid viscous damper.


Introduction
The concept of pre-engineered metal buildings was introduced for the first time in 1917 when The Austin Company, located in State of Ohio, included 10 pre-engineered commercial building designs in their catalogue. It was a complete shift in construction industry at that time. During WWII, US Army used them as aircraft hangers and portable barracks. During late 1960s, standardized building designs were first marketed as PEBs. After 1980s, it dominated the low-rise non-residential buildings market in USA, Europe, and Middle East. The application of PEBs increased throughout the world after 1990s. The concept entered the Indian construction industry in late 1990s, and its current growth rate is at 12-15% per year. A preengineered building (PEB) refers to a building which is pre-designed at a factory using some simulation and modelling software as per the specifications, codes, and the loads before production of the building components and then finally assembled at site, thereby reducing the completion time and are erected in about 6-10 weeks [1,2]. It involves the concept of pre-designing and pre-fabrication processes. With the bending moment diagram's shape, its Page 3 of 29 183 The various components of the pre-engineered building are discussed as follows.
Primary structural members: Primary members are the main load-bearing members of PEB. It consists of the main rigid frame of PEB. These "I"-shaped members are tapered or built-up using hot-rolled plates. Vertical members are known as columns and horizontal members are known as rafters.
Secondary structural members: Secondary members consists of "Z-" and "C"-shaped cold-formed structural members which includes purlins for roof, eave struts and girts for wall. Cold-formed members are called so as there is no cutting, welding, and grinding processes involved. They are made directly by pressing the steel coil in a pressing machine to get the essential shape.
Sheeting/cladding: Sheeting or cladding includes rollformed profiled sheeting for roof and wall. These are color coated, galvalume or galvanized steel ribbed panels.
Bracings: Bracings are provided along the length of the building to provide longitudinal stability in that direction. They are used to transmit lateral forces due to wind, earthquakes, etc. to the bases of column and finally to the foundations. Some of the common types of bracings are diagonal bracing (cable or rod bracing, angle bracing and pipe bracing), portal bracing, knee bracing and diaphragm bracing.
Strut tube: Strut tubes are linked to the bracing system at proper heights to reduce the unbraced length and adjust the allowable stress. They also resist force in the direction of its length.
Flange Brace: It is an angle member ranging between purlins or girts to the inner flange of columns or rafters. It provides them with lateral support and stability.
Foundation: It is the substructure which supports a building or other structure and is usually constructed in concrete. Design of foundations requires.
i. The bearing capacity of the soil and ii. The column reactions of the steel building.
Generally, a foundation structure comprises of spread footings and a slab on grade. It must be designed for both vertical and horizontal loads caused by gravity, wind, earthquake, etc. Hairpins (reinforcement bars) can be used to distribute forces from the column foundation to the floor slab and it results in more economy.
Sag rod: It is a tension member used to limit the deflection of a purlin or girt in the direction of its weak axis. After providing sag roads, sheeting is installed. Its spacing depends on purlins/girts length, loads acting on them and their tributary area.
Mezzanine floor: It is the intermediate floor provided in multi-level PEB structure. It includes profiled steel deck, joists (hot-rolled sections) in the lateral direction, beams (built-up sections) in the longitudinal direction and intermediate support columns.
Anchor bolts: These are used to connect primary structural members to the concrete floor or foundation.
Accessories: It includes the aesthetic components such as fascia to enhance wall appearance, canopy as overhanging roof structure, louvers as wall opening with slanted blades to allow air flow, parapet, roof extensions, skylight & turbo vent.
In the field of steel frame buildings extensive literature is available investigating its performance subjected to wind, seismic and blast excitations. Lee and Foutch [3] evaluated the steel connection failures and proposed safety levels to occupy buildings prior to repair under seismic excitations. Saleem and Qureshi [4] optimized the cost of steel buildings with the use of pre-engineered buildings. Thomas and Krishnakumar [5] evaluated the performance of PEB systems equipped with harp and perimetral bracings subjected to seismic excitations. The post-buckling failure of pre-engineered steel buildings subjected to cyclic loading in the form of incremental dynamic analysis was conducted by Bagatini and Yang [6]. The performance of various bracing placement techniques in mitigating the performance of industrial shed under wind excitations has also been studied by [7]. Qin et al. [8] developed fragility curves for industrial steel buildings exposed to cyclonic winds. The studies reveal that in case of industrial steel buildings wind loading has found to be more critical in comparison with the other dynamic loadings [9][10][11][12]. The study conducted by Milner et al. [13] showed that conservative predictions of PEB's structural performance subjected to vapor cloud explosions (VCEs) was observed in single degree of freedom (SDOF) analysis, whereas significantly better performance of the structure was predicted with advanced computational techniques such as finite element analysis (FEA) and computational fluid dynamics (CFD). Stea et al. [14] performed six tests, each of 900 kg of nitro-carbo-nitrate as explosive and concluded that PEB structures can be used as protective structures since they can withstand incident blast pressures of approximate 3.45 kPa and with additional adjustments their blast resistant capacity can be increased to 13.8 kPa. Similar tests conducted by Dobbs et al. [15] also showed that PEBs can be used as protective structures whereas some modifications are required to confirm the blast resistant capacity of each structural members. Kavitha et al. [16] outlined the process to analysis and design a preengineered industrial building of dimensions 30 m span and 10 m eave height subjected to dead load, live load, wind load and earthquake load. Recently, Sah et al. [17] reviewed the analysis steps and design guidelines as per the international standards to be incorporated in designing preengineered building. Hence a limited literature is available evaluating the performance of pre-engineered building subjected exclusively to an earthquake and blast loading in addition to wind loads. Most of the past studies in the field of pre-engineered building focuses on the comparison of pre-engineered building with conventional steel structures [18][19][20][21][22] and is not the scope of the present study. The main objective of the present study is to investigate an existing PEB structure designed primarily for wind loading neglecting the mining actions conducted recently in the vicinity causing damages to the structure. The present study estimates the underground blast-induced vibrations to be applied to the pre-engineered building and the damages incurred in the process. The study also evaluates the performance of the pre-engineered building subjected to four severe earthquakes in the past to compare its behaviour with blast-induced vibrations. Though the building is not susceptible to the earthquakes presently, it is essential for the reviewers to understand the structural behaviour under blast-and earthquake-induced ground excitations. The study proposes passive control technique in the form of fluid viscous damper in mitigating the seismic and blast effects incurred to the pre-engineered building. The other reason to include earthquake excitations is to depict that vibration control techniques developed to mitigate the earthquake vibrations are applicable to blast-induced vibrations also. The study conducts a parametric investigation of the damper placement and damper properties to achieve the most optimum parameter in yielding the maximum reduction of responses and protecting the structure from any failure and future damages.

Methodology
The plan details, dimensions of structural elements and specifications of an existing pre-engineered building is examined. The structure is modelled and simulated with the help of finite element software ETABS version 19.1.0 Build 2420. The structure under discussion is an existing industrial PEB located at Nagpur, India, and the structure details are detailed in Table 2. The PEB configuration and plan details are illustrated in Fig. 2. It must be noted that Fig. 2a, b, c, d and e show the roof framing plan, anchor bolt plan, high eave side wall framing elevation, low eave side wall framing elevation, front elevation, and back elevation of the PEB system, respectively. The damper placement location adopted in the present study is shown in Fig. 2g. The reason for placing the damper in the prescribed location is to protect the existing PEB structure from the blast and earthquake excitations. The dampers are installed between grids C-D and F-G connecting the tapered columns along both the longitudinal direction. The dampers were installed without changing the bracings position and existing plan of the PEB structure. The study performed modal analysis of the PEB system and observed that the structural period of the selected PEB system in the first three modes are found to be 0.399 s, 0.372 s and 0.299 s with 97.96% mass excited in the first mode. The loads considered are dead load, live load and wind loads for the successful design of the selected PEB structure. The performance of the selected PEB structure is then analysed under blast and earthquake excitations to understand the damages incurred due to selected ground excitations. The design methodology adopted by the present researchers in mitigating the earthquake and blast effects are represented in Fig. 3 with a flowchart. The time history data of blast-induced vibrations and past seismic excitations are applied on the model to check its resistance against blast and earthquake. The time history data for blast-induced vibrations are developed from the mathematical expressions suggested by Hinman [23] and Carvalho and Battista [24] and depicted in Fig. 4. The current study is carried out for a constant value of charge mass (Q) = 50 tonnes whereas the distance from charge point (R) is varied from 100 to 400 m at every interval of 100 m. Thus, Blast 1 has a charge weight of 50 tonnes and charge distance of 100 m, similarly Blast 2 has a charge weight of 50 tonnes and charge distance of 200 m, Blast 3 has a charge weight of 50 tonnes and charge distance of 300 m, and Blast 4 has a charge weight of 50 tonnes and charge distance of 400 m. The time history ground acceleration blast data are generated from the study by Raikar and Kangda [25] and the soil parameters considered are referred from the study by Kumar et al. [26]. The earthquake data include seismic records of Imperial Valley earthquake (magnitude 6.6, 1979), Loma Prieta earthquake (magnitude 6.9, 1989), New Zealand earthquake (magnitude 6.2, 2011) and Northridge earthquake (magnitude 6.7, 1994) as studied by Kangda and Bakre [27] in the past and represented in Fig. 5. The model is then analysed by performing nonlinear dynamic analysis and the critical joints and members are identified. The joint displacement, absolute acceleration and brace force are evaluated under selected ground motions. It is found that many members of the PEB collapsed and damaged under the selected seismic and blast loadings and a need to retrofit the PEB system by strengthening the damaged members or by installing vibration control devices becomes an important action by the concerned structural designers. In the present study, the researchers have opted to install fluid-viscous dampers in three different shapes, namely V shape, inverted-V shape and single diagonal shapes with different coefficients of damper (cα) and damper exponents (α) to improve the performance of PEB structure against blast and earthquake effects. Parametric research is conducted to evaluate the most optimum damper configuration in mitigating the damaging effects of blast and earthquakes. The following codes are adopted for loading and analysis:  [33].

Modelling an existing Pre-Engineered Building in ETABS
Analyse the PEB under dead load, live load and wind load.
Analyze the PEB subjected to blast and earthquake excitations.
Identifying the critical joints and members and finding out the joint displacement, absolute acceleration, and brace force.

Retrofit the damaged PEB by installing fluid viscous dampers.
Varying the damping properties of the viscous damper and placement configurations.

Damper details
Dampers are the devices that allow the building to move elastically and dissipate the energy of earthquake. Seismic dampers permit the structure to resist severe input energy and reduce harmful deflections, forces and accelerations to structures and occupants. They are tactically placed in building structure to control the joint and shear displacements, joint accelerations, brace forces, provide comfort occupancy and resist against wind, blast, and earthquakes. The energy generated by the effects of seismic events and displacements of structural components are absorbed by the dampers. The absorbed energies are dissipated in the form of heat energy. The controlling devices are used in buildings, bridges, aircraft hangers, towers, high rise structures and industrial structures. The different types of dampers commonly employed in the field of engineering are illustrated in Fig. 6 and discussed as follows. The technical specifications (i.e. coefficient of damper c α (kNs/m) and damper exponent (α)) of the dampers are illustrated in Figs. 7 and 8.
i. Fluid Viscous Dampers: In this type of damper, silicone-based fluid passing between piston-cylinder arrangement absorbs the seismic energy. It reduces high wind and seismic activity-induced vibrations [34]. ii. Viscoelastic Dampers: It consists of an elastomer in combination with other metal parts and dissipates the energy by changing into heat energy. It can be used in tall buildings [35]. iii. Friction Dampers: It consists of various steel plates sliding against each other in reverse directions. Here, the energy is dissipated by means of friction between the surfaces [36]. iv. Tuned Mass Dampers: It is a passive control device also known as vibration damper. It is mounted to a specific location in the building or structure to reduce the vibrations induced by wind or seismic events. They are used in automobiles, power transmission and high-rise buildings [37]. v. Magnetorheological Damper: It is a shock absorber which consists magnetorheological liquid which is controlled by a magnetic field [38]. vi. X-plate Damper: It is a device that can withstand multiple cycles of steady yielding deformation, resulting in a high level of energy dissipation or damping [39]. vii. Electromagnetic Inertial Mass Damper: It has been employed as an energy dissipation device for seismic response control due to its ability to generate a large inertance and provide adjustable electromagnetic (EM) damping [40].
The damper properties prescribed in the study have varying values of rubber thickness (RT) of neoprene pad and drop height as shown in the Figs. 7 and 8, respectively, for different types of dampers, namely class A and class B. The damper piston end (DPE) and damper fixed end (DFE) measured peak acceleration and measured shock pulse duration values are derived from the experimental tests conducted by Narkhede and Sinha [41]. The experimental investigation also showed that the accelerations at the damper piston end are significantly lower than the applied acceleration due to a half-cycle sine shock at the damper fixed end. This highlights the ability of fluid viscous dampers to attenuate large-amplitude shocks. Figures 7 for damper class-A and 8 for damper class-B show that shock attenuation is greater for high amplitude shocks and with shorter shock duration. The class A and B damper properties depend on the experimental half-cycle sine shock excitation test study, and it is noted that the DFE of class B dampers is less than that observed for class A dampers. In the present study, the Maxwell model is used to predict the behaviour of fluid viscous damper. ETABS computer package adopts the Maxwell model to simulate the behaviour of a damper. As per guidelines provided in the ETABS the stiffness of the damper element is calculated using the relationship λ = C/K where λ is the relaxation time, C is the damping constant at zero frequency and K is the storage stiffness of the damper at infinite frequency as discussed by [27].

Load calculations
The present study adheres to the Indian Standards to calculate the dead load, live load and wind loads developed in the PEB structure. The detailed summary of load calculations is elaborated as follows:

Dead Load
Weight of each structural element is considered directly in ETABS as self-weight. Weight of purlin = 5 kg/m 2 = 0.05 kN/m. 2 Weight of sheeting = 5 kg/m 2 = 0.05 kN/m. 2 Collateral loads (ceiling, HVAC duct and lighting) = 0.15 kN/m. 2 (Table 1 Table 3 highlights the factors considered in the present study to calculate the design wind speed. Design wind pressure:  Importance factor for the cyclonic region 1.0 Clause 6.3.4, Page-8 The wind load coefficients as detailed in the IS 875 Part-III 2015 are summarized in Fig. 9 and Tables 5, 6, 7, 8, 9, 10, 11 and 12 for various wind load cases and applied to the selected PEB structure. To obtain uniformly distributed load value, calculate the value of P d and then multiply it by Bay spacing and coefficient, i.e. (C pe -C pi ), as detailed in the prescribed tables.
The different wind load cases are summarized as follows: Wind pressure coefficients acting on the structure for different cases        Table 4, Clause 3.5.1 and 5.3.3, the following load combinations are generated to design the selected PEB system. A total of seventeen load cases as shown below are developed to design the PEB system for the critical cases of load combinations.

Analysis of PEB using ETABS
ETABS stands for extended three-dimensional analysis of building system. It is a product of CSI (Computers and Structures Inc.). It is a 3D integrated software that is utilized for structural analysis & design objectives in fields of civil engineering. This software consists of multiple country standards, including latest IS codes. The load combinations as discussed in the previous sections are analysed to obtain the PEB component sections as summarized in Table 13.
The steps involved in the time history analysis of the PEB structure subjected to the blast and earthquake loadings are discussed further as follows: Modelling Steps Analysis: ▪ Step-1: Open ETABS software and enter the grid system data (48 m x 15 m).
(a) Materials Properties: Fe-345 (According to Indian Standards) (b) Section Properties-Frame Sections: Tapered I-Section Column: Using non-prismatic section shape.  Step-7: Design-The PEB system in accordance to IS 800: 2007 and apply the necessary checks for stability and strength.
The members sizes tabulated in Table 13 are adequate and further investigations for blast and earthquake excitations is carried further using ETABS application. The Indian subcontinent has been affected by the Bhuj earthquake in the recent past but the selection of the time histories for the present earthquake analysis is purely to compare the behaviour of the PEB system equipped with and without fluid viscous dampers. The unavailability of many Indian earthquake time histories is also one of the reasons for selecting the earthquake data from other regions. The main scope of the study is to evaluate the performance of PEB system under blast-induced vibrations. The earthquake section is added to compare the efficiency of the selected passive control technique subjected to blast and earthquakeinduced vibrations.
▪ Step-8: Define blast and earthquake ground excitations. To protect the structure, fluid viscous dampers are installed within in the system to retrofit it against the seismic and blast effects and following steps are followed to install viscous dampers within the PEB system as shown in Fig. 10 depicting the critical joint and axial forces developed in the bracing system. The comparison for the blast and seismic responses of the selected PEB system are compared for the shown critical joint and brace element for with and without damper conditions. The dampers were installed without changing the bracings position and existing plan of the PEB structure. The position of dampers placement can be observed in Fig. 2

Results and discussion
The prime aim of the present study is to investigate the performance of an existing pre-engineered building constructed in the city of Nagpur, India, using finite element tool such as ETABS. The study validates the design checks and safety of the structure against the wind effects prevailing in Nagpur city. The study is extended further to understand the structural behavior under the threat against underground blastinduced vibrations and the detrimental seismic tremors that occurred in the past. It is observed the pre-engineered building fails under the selected blast and earthquake time histories. The onus to protect and retrofit the PEB system is on the present structural engineers. The PEB system designed primarily for wind loading conditions as discussed in the previous sections failed under the effects of earthquakes and underground blast-induced vibrations. From Table 14 it is observed that for close range blasts the maximum damage is incurred to the selected PEB system as the maximum members including tapered columns, rafters and all the bracing systems failed to meet the safe design limits and need to redesign or protect them with the help of passive control is suggested. In the present study the later technique is incorporated for the safety of the PEB system. For blasts at 200 m the PEB bracing system and a few tapered columns proved to be unsafe whereas for blasts at 300 m the bracing system and a couple of columns of the PEB structure are in critical damage state. In the case of far end blasts at 400 m only the bracing systems got damaged and failed. The present study also studied the performance of the selected PEB system under the past devastating earthquakes to understand its behavior and damage pattern in comparison with the blast-induced vibrations. It is observed that for all the selected seismic excitations the bracing systems of the PEB failed with the maximum damage incurred under the recently New Zealand earthquake wherein many tapered columns also failed. Thus, the present study provides an important insight on the performance of the PEB system subjected to blast and earthquake shaking that has been missing in past studies. The installation of the fluid viscous dampers protects all the members of the PEB system when subjected to blast and earthquake excitations. The design results show that all the members passed the serviceability checks when the PEB system is installed with fluid viscous dampers. The authors of the present study adopted fluid viscous dampers at the selected locations of the PEB system to prevent its failure. It is observed that the installation of the viscous dampers within the PEB system prevents the failure of the critical members of the PEB system. The next objective of the present study is to evaluate the efficiency of the available fluid viscous dampers. A total of 12 viscous dampers were selected to evaluate the most effective damper property in mitigating the individual blast and earthquake effects. Six dampers belong to damper class A and six to damper class B as detailed in the previous section. All the 12 dampers are further placed in three different shapes, namely V-shaped, inverted-V and single diagonal individually to the PEB models to note the effectiveness of placement on the performance of the selected PEB system. Each PEB model is equipped with 12 different technical specifications of damper having different coefficients and exponents. It must be noted from the study that placing the damper in the PEB system prevents the failures of the tapered columns and bracing as observed in the Tables 14 and 15. The study conducts the re-assessment of the PEB system with fluid viscous dampers to conclude that the required safety and serviceability limits of the PEB are within limits when installed with selected fluid viscous dampers. The installation of the fluid viscous damper in the PEB structure against the blast and earthquake loading is an efficient approach. Next, the nonlinear dynamic analysis is performed to determine the critical joint displacements, absolute acceleration, and member brace force under all cases of blasts and earthquakes. The study also evaluates the damper energies and damper hysteresis curves to understand the damper behavior in reducing the responses of the PEB system. Tables 16 and 17 compare the performance of class A and class B fluid viscous dampers in mitigating the blast-and earthquake-induced displacements at the critical joint of the PEB system, respectively. It is observed that the A-3 damper and B-1 damper yields maximum reduction in responses when placed in the form of V-shape as compared to the other selected placement techniques in their respective damper class segment. The joint displacement of the PEB system reduced in the range of 38-44% for close range blasts and 50-60% for far end blasts when equipped with inverted V-shaped damper. For V-shaped and diagonal placement reductions are in the range of 39-45%, 51-64% and 33-36% and 41-53%, respectively. Thus, proving that V-shaped placement is the most effective technique in mitigating the blas-induced vibrations. Under the seismic excitations also the V-shaped placement showed the maximum reduction in responses in the range of 70-83%, 62-80%, 46-50% and 47-73% for Imperial Valley, Loma Prieta, New Zealand, and Northridge earthquakes, respectively. The overall comparison of the efficiency of the damper under blast and earthquake excitations show that fluid viscous dampers are most effective under seismic motions. The study also reports that B class dampers yields reductions in the range of 44-54% and 65-71% under close and far detonated blast excitations. The efficiency of the fluid viscous dampers when subjected to earthquake excitations is further improved and are in the range of 70-85% for the selected seismic actions. The New Zealand earthquake reports minimum reduction in displacement in the range of 27-32%, 41-44% and 5-16% for inverted V-shaped, V-shaped, and diagonal brace, respectively. Thus, installing the fluid viscous dampers in PEB system is an effective method to protect and enhance its performance. It must be noted that the effectiveness of the damper element increases as the charge distance increases and in case of earthquakes maximum reductions are obtained for short duration Imperial Valley earthquake having the least peak ground acceleration (PGA) of 3.56 m.sec2 as compared to the long duration New Zealand earthquake with a maximum PGA of 7.86 m/sec2. It is finally concluded that selecting the B-1 damper and placing it in the V-shape results in the maximum reduction in responses for all the blast and earthquake generated time histories. From Tables 18 and 19, it is observed that the selected damper technique fails to mitigate the absolute acceleration responses under the far and near occurred blast loadings. However, it is interesting to note that damper A-3 and B-1 prove to play a vital role in mitigating the earthquake responses generated due to Imperial Valley, Loma Prieta and Northridge earthquakes. The selected damper properties and damper placement technique fails to reduce the absolute acceleration responses under long duration New Zealand earthquake. The absolute acceleration reponses are reduced by 50-56%, 35-40% and 19-23% under Imperial Valley, Loma Prieta and Northridge earthquakes, respectively.
Next the study evaluates the critically damaged brace force members under blast and earthquake loadings. The results presented in Figs. 11 and 12 reveal that the A-3 and B-1 dampers installed within the PEB system yield maximum reduction in responses for far and closely occurred blasts, i.e. 400 m and 100 m, respectively. Both V-shape and inverted V-shape dampers are equally efficient in reducing the blast responses. The single diagonal dampers generate 5-20% lesser reductions when compared with V-shaped placement. It is noted from the study that the brace force in the member D8 is reduced by 61-77% and 87-90% for near and far detonated blasts, respectively, when the PEB system is installed with A-3 class dampers placed in V-shaped, inverted V-shaped and diagonal shape. The performance is further improved when B-1 class dampers are used and placed in the selected shapes and the responses are reduced by 71-83% and 90-92% against near and far blasts, respectively. The maximum reductions in the bracing element of the PEB system are observed for V-shaped fluid viscous placement technique. The effectiveness of the PEB structures against far occurred blasts is 20% more than that observed for near generated blasts. The earthquake results for brace force are in unison with that obtained for blast loadings. A-3 and B1 dampers outshines the other damper classes in their respective damper classes and yields maximum reduction in brace force for the selected earthquake excitations. The V-placement of the fluid viscous damper performs better as compared to the other selected damper placement technique. The reductions are in the range of 79-94% for A-3 dampers and 80-96% B-1 dampers. The New Zealand earthquake is found to be the most destructive earthquake yielding minimum reduction of responses when the selected PEB system is equipped with fluid viscous dampers. Next the behaviour of the best damper class such as A-3 and B1 are analysed further by plotting the axial force deformation to understand its role in mitigating the structural responses of the PEB system. It is interesting to note from Figs. 13 and 14 that the force deformation of the single diagonal damper leads to maximum force and deformation to reduce the PEB responses. The inverted V-shaped and V-shaped damper exactly show similar axial deformation behaviour. It is interesting to note that in case of PEB system that the axial force deformation of inverted V and V-shaped damper leads to maximum reduction despite the axial force deformation showing limited values as compared to single diagonal placement technique under all blast and earthquake excitations, respectively. Both A-3 and B-1 class dampers report that the force deformation ability of single     class subjected to all blast and earthquake ground motions as shown in Figs, 15 and 16 for earthquake and blast loadings respectively. It is observed that the energy dissipation ability of the inverted V-shaped damper is lower by 35-50% as compared to that dissipated by single diagonal damper in mitigating the blast and earthquake responses. The results reported in the past showed that the energy dissipation of the dampers played a crucial role in resulting in the maximum reduction in the building responses. The maximum reductions in the structural responses are directly proportional to the force deformation behaviour and energy dissipated by the externally installed damper systems. The present study shows that for a PEB system though the energy and force deformation of the damper system is limited as in case of an inverted V-shape damper placement, but it yields maximum structural responses and is the future scope of the study. The effect of finite element tool on this behaviour needs to be explored and further investigations in this context is essential. Thus, it is finally concluded that fluid viscous dampers are found to be an efficient technique in mitigating the blast and earthquake responses of a PEB system.

Conclusion
In the present study, the authors have investigated the performance of an existing pre-engineered building constructed in the city of Nagpur, India. The PEB structure is designed considering the wind effects and events like blasts and earthquakes are neglected. The earthquake data considered in the present study is obtained from COSMOS database. The structural period of the PEB system is found to be 0.399 s with 97.76% mass excited in the first mode. The blast data are generated by considering a charge weight of 50 tons and varying the change distance in the increments of 100 m. The study incorporated the applicability of passive control techniques in mitigating blasts and earthquake causing damaging effects. The study varies the damping properties of the fluid viscous dampers along with the placement techniques in retrofitting the existing PEB structure. The present study showcased the capability of fluid viscous dampers in protecting and preventing the critical failure of various members of PEB system. The study highlights the retrofitting efficiency of fluid viscous dampers in protecting a PEB system designed initially for wind conditions and damaged during an effect of an unexpected earthquake or blast. The study evaluates the damper placement capability of fluid viscous damper by placing the damper in form of diagonal, V-shaped, and inverted V-shaped placement technique. It is observed that placing the damper in shape of V-shape yields the maximum reduction in responses of the selected PEB system in comparison with diagonal and inverted V-shape damper. The following conclusions are drawn from the investigations: 1. The study evaluates two classes of fluid viscous dampers, namely A-class fluid viscous dampers and B-class dampers. Irrespective of the shape of damper placement, the study reports that the maximum reduction in peak displacement and brace forces of the PEB system are obtained at a damping coefficient of 315 kNs/m and damping exponent of 0.46 for damper class A. In the case of class B dampers, the maximum reductions are obtained for damper B-1 having damping coefficient of 330 kNs/m and damping exponent of 0.36. The maximum reductions in displacement are in the range of 50-60% and 65-75% for class A-3 and B-1 dampers, respectively, subjected to far end blast explosion. 2. The study also evaluated the efficiency of the fluid viscous dampers in controlling the absolute acceleration responses of PEB system when subjected to seismic excitations in comparison with the blast-induced vibra- tions. It is concluded from the study that the A3 and B1 class dampers reduced the acceleration responses by 54%, 40% and 22% under Imperial Valley, Loma Prieta and Northridge earthquakes. The absolute acceleration responses increased with the installation of the fluid viscous dampers when subjected to New Zealand earthquake and all selected blast-induced vibrations. Thus, showcasing the impact of ground motion frequency on the performance of the selected dampers and its inability to reduce the absolute acceleration responses under blast-induced vibrations. 3. The study also investigates the effect of damper placement technique in mitigating the blast and earthquake responses of the selected PEB system. The damper placement shapes include V-shaped, inverted V-shaped and diagonal placement. It is observed that the V-shaped placement reduced the structural displacement and brace force induced in the PEB system by 71% and 91%, respectively, when subjected to far end blasts and infused with B1 class damper properties. The inverted V-shaped dampers reduced the structural responses by 67% and 90%, whereas the diagonal bracing placement showed reductions by 59% and 89%, respectively. 4. It is interesting to point out that the energy dissipation and force deformation of diagonally placed fluid viscous damper showed the maximum capacity in comparison with the other shaped dampers. It must be noted that the V-shaped damped controlled the responses of the PEB system by yielding minimum force deformation and damper energy as presented. Both V-shaped and inverted V-shaped dampers proved to be an effective technique in mitigating the responses of PEB system.

Data availability
The data used to support the findings of this study are included within the article.

Conflict of interest
The authors declare that they have no conflicts of interest.

Ethical approval
The authors did not receive support from any organization for the submitted work. The authors declare that they have not submitted the manuscript to any other journal for simultaneous consideration.

Informed consent
The corresponding author declares consent for publication in the journal of Innovative Infrastructure Solutions.