Nonlinear Static Analysis for Seismic Evaluation of Existing RC Hospital Building

Abstract

Nonlinear Static Analysis otherwise known as pushover analysis will be used in this study to evaluate the seismic performance of an existing reinforced concrete (RC) hospital structure. This method aids in determining the structure’s ability to withstand lateral loads and calculating its local and global deformation requirements. The study begins with a thorough analysis of the geometry, materials, and structural elements of the structure, followed by a review of pertinent building regulations and codes. A finite element model in three dimensions of the hospital building is created, encapsulating the main features of the structure’s behavior under seismic loading. The lateral force method of analysis and static pushover analysis is then carried out and compared, and the findings are used to pinpoint crucial weak places, potential failure mechanisms, and regions needing additional research or fortification. Recommendations are given to improve the seismic performance of the current RC hospital building based on the pushover analysis’s findings. These adjustments can be made to the structural system via retrofitting techniques or to non-structural elements. For engineers, architects, and legislators concerned with the seismic assessment and renovation of hospital buildings and other crucial infrastructure, the findings from this study are valuable.

1. Introduction

In recent times, the prioritization of evaluating vulnerabilities and potential hazards arising from seismic events has gained significance, largely due to the construction of numerous structures that do not adhere to relevant seismic regulations [1,2]. The resulting damage from seismic occurrences has proven to be substantial [3]. It is imperative to examine existing structures in the context of potential seismic threats, given the risks these events pose to both human lives and the socio-economic framework. This impact influences the resilience and preparedness of buildings for such catastrophic incidents. An area of utmost concern in this evaluation is the seismic assessment of structures, with a particular focus on hospitals [4]. The primary objective of seismic design and evaluation is to ensure the safety and preservation of lives, minimize damage to infrastructure, and maintain the operational continuity of vital institutions such as hospitals. These establishments are intricate in nature, serving roles comparable to hotels, offices, and laboratories, as well as storage for both perishable and hazardous materials [5]. However, this complexity renders them particularly susceptible to the effects of seismic disturbances. Their vulnerability emanates primarily from two aspects: the structural integrity of the building and the ability of healthcare personnel to manage a sudden surge in patient numbers.

Past seismic incidents, such as the 1994 Northridge earthquake, underscore the extensive devastation that earthquakes can inflict upon hospitals [6]. Subsequent studies following these events highlighted significant water damage, attributed to failures in chiller and hot water pipelines, even in the absence of structural harm [7]. Failures in non-structural components, including fire sprinkler systems, greatly hindered operational capabilities. Such occurrences underscore the critical need for comprehensive earthquake preparedness plans within hospitals. These plans should encompass efficient evacuation procedures, alternative healthcare facilities, and strategies to manage substantial increases in patient numbers [8]. The necessity of anticipating the seismic response of buildings considering potential earthquake impacts is evident. A multitude of analytical and experimental studies elaborate on this concept [9]. The utilization of nonlinear static analysis for evaluating structures brings forth notable benefits. In comparison to methods such as Rapid Visual Screening [10], this approach offers a comprehensive and deterministic assessment of a building’s behavior during seismic events. Furthermore, relative to nonlinear dynamic methods [11], this approach is less complex and more straightforward, rendering it particularly suitable when time and resources are constrained.

In Hungary, medical establishments warrant heightened attention among all essential structures. Interestingly, many Hungarian buildings were constructed during periods when seismic codes were not rigorously adhered to, revealing the potential seismic risks they might face. The novelty of the current study lies in its comprehensive methodology for seismic assessment, which specifically targets Hungarian medical facilities—a domain that has been previously overlooked. By amalgamating internationally recognized methodologies with considerations specific to the region, the objective is to furnish a tailored framework for comprehending and mitigating seismic vulnerabilities within Hungarian healthcare infrastructure. This nuanced approach, grounded in both global best practices and local intricacies, holds the promise of delivering actionable insights that are not only robust but also pertinent to the region. However, it is important to acknowledge that studies solely focused on Hungarian medical infrastructures are limited. Consequently, our research relies heavily on investigations that center around Italian and international medical facilities, as referenced in [1,6,7,8,12,13]. These studies underscore the inherent seismic vulnerabilities within such pivotal infrastructures, which play a pivotal role during seismic events.

With the incorporation of the Knowledge Level 2 concept, this study endeavors to spotlight the seismic assessment of an actual structure using the nonlinear static analysis method, with the potential to extend its applicability to other regions in the event of seismic occurrences. Operating with a grasp of Knowledge Level 2 [14], our exploration delves beyond basic evaluations while remaining accessible to those without an expert-level understanding. The hospital building under examination is situated in Hungary’s Esztergom Region, categorized as a seismic zone III locale. Further insights into the modeling data for the building can be found in Section 1. The evaluation employs three prevalent seismic analysis techniques from Eurocode 2, detailed in Section 3. For modeling and analysis, the primary tool employed is the software program Seismostruct [15], while SAP2000 is utilized for specific modal analysis aspects. The overarching aim of this study is to provide insights into the execution of nonlinear static analyses on reinforced concrete hospital structures, with the potential for replication in other regions to enhance earthquake preparedness.

2. Description of the Analytical Model and Details of the Investigated Building

In this study, we meticulously assess Building Number 7, located within the premises of the Vaszary Kolos Hospital Facility, which was established in the year 1975. Our analysis is founded on the original design plans, with a strong emphasis on its alignment with Eurocode standards [16]. The methodology of Knowledge Level 2 [14] has been adopted, reflecting a comprehensive understanding of the overall design and specific dimensions. This comprehension has been derived primarily from preliminary construction sketches utilized during both the initial construction phase and subsequent adjustments. Our grasp of structural intricacies has been further bolstered via meticulous on-site inspections focusing on key components to ensure congruence with actual conditions. The mechanical attributes of the materials have been gleaned from initial design specifications, supplemented via on-site tests to validate their properties. This knowledge level allows us to use any method of analysis with the confidence level determined at 1 and 2.

To assess the structural performance of Building Number 7, we have undertaken an evaluation using both the Equivalent Linear Static and Nonlinear Static analysis methods. These methods enable a thorough examination of the building’s behavior under seismic loads, providing insights into its response characteristics and vulnerabilities.

1.

General Overview and Imagery

The building in question falls under the category of a four-story reinforced concrete movement-resisting frame construction. It is characterized by the presence of concrete beams and columns designed to withstand both lateral and vertical loads. This classification aligns with the FEMA P-154 categorization, specifically denoted as a C1 type building [17]. The building’s dimensions are detailed as 17.4 m in the Y direction and 23.7 m in the X direction. The heights of the individual stories are as follows: the ground floor stands at 2.53 m, while the subsequent floors and the roof maintain a uniform height of 3.1 m. The plan of the building is in the form of a T-shape.

For a comprehensive visual representation, please refer to the accompanying imagery and diagrams—Figure 1 for the satellite view, Figure 2 for the site plan, Figure 3 for the floor plan, Figure 4 for the 3D model of the building, and Figure 5 for a photograph of the actual building.

2.

Principal Structural Components

The structural components of the building are outlined in

Table 1. Principal structural components.

Component	Details	Reinforcement Size	Additional Info
Slabs	20 cm thick	∅10 mm bars at 10 cm spacing	Both X and Y axes
Beams	0.5 m width, 0.4 m depth, 6.0 m avg length	su4 ∅14 mm, sl2 ∅14 mm, ss2 ∅12 mm, etc.	Transverse reinforcements every 15 cm
Columns	0.42 m × 0.42 m	Longitudinal: 4 ∅20 mm (corners), 2 ∅16 mm (sides)	Transverse: ∅10 mm at 10 cm
Shear Walls	Outer: 240 mm; lift cores: 120 mm	-	-
Masonry Infill Walls	-	-	Designed using the equivalent strut model [18]

, highlighting their respective details, reinforcement sizes, and additional relevant information. These components encompass slabs, beams, columns, shear walls, and masonry infill walls. Detailed specifications of the dimensions, reinforcement sizes, and arrangements of these elements are provided for a comprehensive understanding.

3.

Load Considerations

Table 2. Building load considerations (kN/m²).

Table Description	Structural Component	Area	Dead Load	Live Load
Dead Loads	Roof		0.25
Dead Loads	Floors		3.0
Dead Loads	Walls		1.0
Dead Loads	Partitions		0.15
Dead Loads	Staircases		4.0
Dead Loads	Elevator Core		3.0
Live Loads		Patient Rooms		3.0
Live Loads		Corridors		4.0
Live Loads		Operating Rooms		5.0
Live Loads		Waiting Areas		2.5

outlines the various load types and their respective magnitudes based on Eurocode guidelines for hospital buildings. This includes dead loads, which accounts for the inherent weight of the structure, as well as live loads that vary according to different areas of the building.

The building’s main structural elements are detailed in Table 1. In addition to typical specifications, special attention was given to shear capacities due to their significance in seismic behavior. In particular, critical areas such as beam-column joints and shear wall intersections were closely monitored for shear demands during the analysis to ensure the structure’s seismic integrity.

4.

Materials and Analysis Specifics

Concrete and Steel: Ref. [19] defines the longitudinal reinforcement material in SeismoStruct [15]. The concrete model from J.B. Mander et al. [20] is used, with an average strength of 20 MPa, potentially reducing to 16 MPa [21]. Class S500 steel is employed [22], with safety factors γc = 1.5 for concrete and γs = 1.15 for steel.

Seismic Analysis: The N2 method from [23] and Eurocode 8 Type 2 Spectra [24] are integrated. The Peak Ground Accelerations (PGAs) are 0.36 g, 0.12 g, and 0.09 g, respectively [25]. Based on a PGA of 0.12 g, soil type C, and a 5% damping ratio, the earthquake response is mapped in Figure 6. Eurocode soil type 8 was found to be the most common in the region [26].

Table 3. Performance requirements and compliance requirements for each limit state.

Limit State	Definition	Return Period
Damage Limitation (DL)	Structure lightly damaged with structural elements retaining their strength and stiffness. Non-structural elements show initial signs of cracking; economic losses are minimal. No permanent drifts.	Probability of exceedance 20%/50 years–225-year return period
Significant Damage (SD)	Significant damage to the structure, residual lateral strength, and stiffness is evident. Damage to several non-structural elements. Moderate permanent drifts.	Probability of exceedance 10%/50 years–475-year return period
Near Collapse (NC)	Heavy damage to the structure, low residual lateral strength, and stiffness. Many non-structural elements have collapsed. Large permanent drifts were observed.	Probability of exceedance 2%/50 years–2475-year return period

summarizes performance requirements and compliance criteria for each limit state [24].

3. Numerical Modelling and Analysis

Seismic effects and effects of other actions in the seismic design circumstances are determined using the following methods according to [14,27].

1.

Lateral Force method of analysis—applicable to buildings meeting the requirements stipulated in [24] 4.3.3.2.1. This method has been applied in this study to determine the structure’s base shear force, which will be used as the nominal load on the structure.

2.

Modal Response Spectrum Analysis—relevant to all building types as stipulated in [24] 4.3.3.3.

3.

Nonlinear Static Pushover Analysis—according to Section 4.3.3.4.2 of [14].

4.

Non-linear time history (dynamic analysis according to Section 4.3.3.4.3 of [14].

In this study, the lateral force method of analysis has been carried out manually, following the relevant criteria as specified in [24], Seismostruct 2023 has been used to carry out the eigenvalue and pushover analysis.

3.1. Lateral Force Analysis Procedure

Eurocode 8 adopted the Lateral Force Method (LFM) for seismic design, focusing on linear static analysis of structures under orthogonal horizontal forces. The applicability depends on factors such as buildings’ fundamental period and elevation regularity. LFM converts peak base shear into lateral inertia forces, aiming to balance simplicity, intuition, and seismic response prediction accuracy [4].

Where m is the total mass of the building, $S_d\left(T_1\right)$ is the ordinate of the design spectrum, $T_1$ is the structure’s fundamental vibration period, and $\lambda$ is the correction factor.

The seismic analysis adheres to the fundamentals of [27]. Applying the values, the weight of the structure, m = 15,898.26 kN, ordinate of the design spectrum at period T₁, S_d (T₁) = 0.92, the correction factor, 𝜆 = 0.85. The value of the base shear equals 12,432.44 kN which seems to be a little rough and overestimated. Therefore, we opted to apply the program-generated values from SAP2000 [28]. The results from the manual analysis can then be compared to those autogenerated by the program as shown in

Table 4. Program-generated load patterns.

Load Pat	Corr Fact	T Used	Coeff Used	Weight Used (kN)	Base Shear (kN)
EQx	1.0	0.4006	0.6	15,898.26	9212.586
EQy	1.0	0.4006	0.6	15,898.26	9212.586

.

For our study, the seismic base shear force for the principal X and Y directions were considered equal and calculated using the expression (Eurocode 1998-1 Eqn 4.5):

$$F_b=S_d\left(T_1\right)\ast m\ast \lambda ,$$

(1)

3.2. Nonlinear Static Analysis

Static Pushover Analysis has been widely implemented in determining the nonlinear response of structures and thus their vulnerability [29]. Its application has been recommended in various codes, including [30,31,32], among others. It has also been considered an effective tool for evaluating both existing and new buildings. Its correct use gives the users proper information about the expected performance of the building and its components. Mass proportional and force-controlled load patterns are usually recommended in various codes to obtain the capacity curve. The structure’s pushover seismic performance was evaluated in the -X direction and Y direction. Figure 7 and Figure 8 depict the matching pushover curves. It was observed that the structure’s response in the Y direction was larger than that of the X direction.

The markers in the capacity curve indicate instances when significant actions start to take place on the structure. These range from the first crush of the confined concrete to the absolute maximum capacity stage of the curve where the total collapse of the reinforcement materials starts. The bilinearized capacity curve is shown in Figure 9; the corresponding performance points are also indicated on the curve showing the different limit states. For our study, we decided to use capacity curve values from the X direction. Nonlinear static procedures, such as those outlined in ATC 40 [32], FEMA 356 [14,24,33,34] among other codes, are used to evaluate the seismic performance of buildings by incorporating the nonlinear force-deformation characteristics of individual components and elements due to inelastic material response. These procedures use a pushover curve (Figure 7 and Figure 8), which is a curve of base shear versus top displacement, obtained by subjecting the building model to monotonically increasing lateral forces or increasing displacements until the building collapses [35].

The maximum displacements that are likely to be experienced during a given earthquake are determined using either highly damped or inelastic response spectra. The advantage of these procedures over linear procedures is that they directly consider the effects of nonlinear material response, resulting in calculated internal forces and deformations that are more accurate approximations of those expected during an earthquake [33].

S_a represents the spectral acceleration at point S_d. S_d denotes spectral displacement. V signifies the base shear in a pushover analysis at roof displacement, known as ∆_roof. ∆_roof represents the displacement in a pushover curve. There are two fraction terms, PF₁ and α₁. α₁ symbolizes the modal mass coefficient during a pushover analysis. PF₁, on the other hand, describes the first natural mode’s modal participation factor.

Performance Point and Capacity Spectrum

To position the pushover results attained via the N2 method adopted in Seismostruct, the results are plotted against the Acceleration–Displacement Response Spectra (ADRS) format (S_a vs. Sd) as outlined in [36].

This requires the application of various equations to effect the required transformation.

$$P{F}_1=\left[\frac{{\sum }_{i=j}^N\left(w_i{\varnothing }_{ij}\right)/g}{{\sum }_{i=1}^N\left(w_i{\varnothing }_{i1}^2\right)/g}\right],$$

(2)

$${\alpha }_1=\frac{{\left[\left(w_i{\varnothing }_{ij}\right)/g\right]}^2}{\left[{\sum }_{i=j}^N{w}_i/g\right]\left[{\sum }_{i=1}^N\left(w_i{\varnothing }_{i1}^2\right)/g\right]},$$

(3)

$$S_d=\frac{V/W}{{\alpha }_1},$$

(4)

$$S_a=\frac{{\Delta }_{roof}}{P{F}_1{\varnothing }_{roof,1}},$$

(5)

$\varnothing$_i and $\varnothing$_roof represent the shape of the mode under analysis during a pushover at location i and at the roof, respectively. W_i is the weight acting at location i. W is the total weight of the structure. Lastly, N is the total number of discrete locations where the weight and pushover mode shape are considered.

To transform a demand spectrum from the S_a and T format into the ADRS format, it is necessary to calculate the S_d value for each point on the curve via the specified equation.

$$S_d=\frac{1}{4{\pi }^2}{S}_a{T}^2,$$

(6)

From the analysis conducted, the capacity curve is translated into spectral acceleration and spectral displacement coordinates. This transformation gives rise to the capacity spectrum, which serves as a tool to assess the intended seismic performance of the structure. By overlaying the demand spectrum onto the capacity spectrum, we accelerate this process. According to the data depicted in the accompanying diagram, the structure demonstrates substantial deformation capability up until a displacement of approximately 0.08 m. This is the point at which the structure’s stiffness starts to deteriorate significantly, marking the transition into the ductile behavior phase.

Table 5. Modal Participation Factor for the first natural mode.

Floor Level	Height	Wi	${\varnothing }_{\mathit{i}\mathit{j}}$	g	(Wi𝜙i,j)/g	𝜙ij^2	(Wi𝜙i,j^2)/g	PF1
Roof	14.93	981.84	1	9.81	100.0856	1	100.0856	1.359500955
4	11.83	3814.25	0.87	9.81	338.2668	0.7569	294.2921
3	8.73	3814.25	0.74	9.81	287.7212	0.5476	212.9137
2	5.63	3814.25	0.61	9.81	237.1756	0.3721	144.6771
1	2.53	3473.67	0.48	9.81	169.9655	0.2304	81.58344
∑		15,898.26			1133.215		833.552

and

Table 6. Modal mass coefficient values.

Floor Level	Height	Wi	${\varnothing }_{\mathit{i}\mathit{j}}$	g	(Wi𝜙ij)/g	${\varnothing }_{\mathit{i}\mathit{j}}$^2	(Wi𝜙i,j^2)/g	((Wi𝜙i,j)/g)^2	Wi/g	(Wi𝜙i,j^2)/g		α1
Roof	14.93	981.84	1	9.81	100.0856	1	100.0856		100.0856
4	11.83	3814.25	0.87	9.81	338.2668	0.7569	294.2921		388.8124
3	8.73	3814.25	0.74	9.81	287.7212	0.5476	212.9137		388.8124
2	5.63	3814.25	0.61	9.81	237.1756	0.3721	144.6771		388.8124
1	2.53	3473.67	0.48	9.81	169.9655	0.2304	81.58344		354.0948
∑		15,898.26			1133.215		833.552	1,284,176	1620.618	833.552	1,350,869	0.950629

provide the values for the PF₁ and α₁ for the structure.

Eventually, the structure succumbs to failure when the displacement reaches 0.29 m. At this juncture, the base shear, which is the total horizontal force experienced by the structure, amounts to 10,871.69 kN. This level of force, combined with the deformation experienced, leads to the permanent collapse of the structure.

This is depicted in Figure 10. Beyond the standard steps of the pushover analysis, special attention has been given to potential shear failures. As the structure is loaded incrementally, the shear demand in each member is compared with its shear capacity. Shear vulnerabilities, especially in critical zones such as beam–column junctions and wall bases, are monitored closely. Identifying and addressing these vulnerabilities is paramount, as premature shear failures can drastically alter the seismic response of the structure.

3.3. Nonlinear Plastic Hinges and Chord Rotation Capacity Checks

Structural models use non-linearity qualities, using plastic hinges at terminal sections. Inelastic processes for beams are simple bending, while columns have a combination of axial and bending stress [37]. Plastic hinges are specified according to FEMA 356 standards [33]. Figure 11 illustrates this relationship. During a pushover analysis, a member’s behavior can be guided by either deformation-controlled (exhibiting ductility) or force-controlled (demonstrating brittleness) actions. The force–deformation response of the hinge is characterized using five reference points, namely A, B, C, D, and E (Figure 11). The verification requirements must be met by the structural demand linked to the given goal displacement. The capacity of chord rotation in the limit condition of near collapse (NC) is the total chord rotation capacity (elastic + inelastic component) of concrete elements under cyclic loads (${\theta }_m$). The chord rotation capacity associated with the severe damage (SD) limit condition is 3/4 of the ultimate chord rotation (SD = 3/4 ${\theta }_m$). The chord rotation at yielding (y) corresponds to the damage limitation (DL) limit condition [38].

3.3.1. Shear Failure Check

In structural analysis, ensuring the safety and reliability of a design is of utmost importance. A critical failure mode to address in this context is shear failure. One of the pivotal metrics used to gauge the structure’s resilience against this mode of failure is the performance ratio. A performance ratio exceeding 1 suggests that the demand on a structural element surpasses its limit, flagging it for potential concern.

Our analysis commenced at step 1, but it was not until output number 7 (with a load factor of 0.897), Figure 12 that we observed the first signs of shear failure. In this instance, the shear wall (W21_1-Sec(a)) was the first to exhibit this vulnerability. As the analysis progressed and the load factor increased, more elements began to show susceptibility to shear failure. By output number 51, with a load factor of 1.27607, an array of elements illustrated potential shear failure, as denoted by their performance ratios. For Output Number 7 with a load factor of 0.897, shear failure initiates, especially with the shear wall being the first to exhibit such concerns, as shown below.

As the analysis progresses, by Output Number 20 with a load factor of 1.2354, Figure 13 the onset of shear failure becomes more widespread, affecting various structural elements as depicted in the following representation:

The situation becomes even more pronounced by Output Number 51 with a load factor of 1.27607, Figure 14. At this stage, a multitude of structural elements indicate signs of nearing or reaching shear failure. This progression is captured below.

The progression from Output Numbers 7 to 51 showcases a significant increase in the number of elements approaching or achieving their shear failure limits. Such insights are invaluable for further design considerations and potential retrofitting measures to enhance structural resilience.

3.3.2. Plastic Hinge Forming

The structure was subjected to a total of fifty-one iterations to assess the behavior of the plastic hinges under monotonically increasing loads. According to the analysis, the plastic hinges were generated initially at the column ends at the fourth iteration, with a load factor of 0.8641; the first yielding of the beams was experienced at the fourteenth iteration where a load factor of 1.253 was applied to the structure, which the load factor represents. The magnitude of a load at any step is given by the product of its nominal value, defined by the user, and the current load factor, which is updated in an automatic or user-defined fashion. These hinges give because of unique design events. Figure 15 represents a sequence of hinge behavior and yielding patterns at various select points of the structure under increasing loads.

The damage textures in the structure are illustrated with various element textures and color codes, including crush_conf, which represents crushing of confined concrete in a structural member), yield (representing the stage where a structural member starts deforming plastically), crush_unc (representing crushing of confined concrete in a structural member), and fracture (representing the point where a structural element starts to break or crack under a given stress).

4. Results and Discussion

Static Nonlinear (Pushover) Analysis was performed for the hospital building in SeismoStruct considering the dead loads and percentage of the live loads (30%). Aimed at analyzing the behavior and performance of the structure when exposed to an earthquake design lateral load, the lateral loads were determined by the lateral force method, this was estimated at 12,432, 44 kN in adherence to the recommendation stipulated in Eurocode 8 Part 2, and the loads generated by SAP2000 which was determined to be 9212.586 kN. The lateral loads generated via the program were selected as the nominal loads for conducting the pushover analysis. Modal analysis was used in determining the values of the mode shapes and amplitudes of displacement at the various floor levels; results are shown in Table 5. Some of the factors considered for this were the seismic actions, existing soil conditions, building characteristics, Importance Class and factor of the structure and the design spectrum type. The Type 2 design spectrum was selected for our analysis. These values were the parameters used for conducting the pushover analysis.

Figure 7 and Figure 8 show the capacity curves based on the pushover analysis in both the X and Y direction. The bilinearized capacity curve shown in Figure 9 for the X direction shows the target displacements for the related pushover analysis in that direction for the three selected limit states. The value of the target displacement for the Significant Damage state is 6.157 mm, and the maximum building capacity in this direction is 10,871.69 kN with a displacement of 47.9 mm. Looking at the capacity in the Y direction, it can be observed that the structure reaches a peak of 26,333.98 kN at a maximum displacement of 3 mm. The N2 Eurocode method was applied for this process. Additionally, for comparison purposes and to put the pushover analysis results into perspective, the capacity spectrum method was also carried out to determine the approximate value of the structure’s performance point. The attainment of this involved a series of procedures which necessitated the conversion of the capacity and demand curves into Spectral Acceleration versus Spectral Displacement (ADRS) format This was mostly conducted manually to aid in a better understanding of the whole procedure. Interpretation of results from the capacity spectrum method showed that there was a large deformation capacity of about 0.29 m observed in the X direction.

It is also observed that there are larger deformations in the X direction (approximately 0.29 m at the peak) than in the Y direction (0.0004 m).

It is observed that several structural members fail when it comes to the established code-based check conditions. This is more prevalent in the X direction. This signifies potential structural vulnerabilities which pose a serious threat to the performance of the building under certain unexpected lateral loadings from future earthquakes. The findings from our pushover analysis resonate with other studies emphasizing the significance of shear considerations. In particular, the potential shear vulnerabilities identified in our building underscore the need for comprehensive shear demand assessment. Such vulnerabilities, if not addressed, could compromise the building’s ability to withstand seismic events, leading to catastrophic consequences, especially for critical infrastructures such as hospitals.

5. Conclusions

The performance of the reinforced concrete hospital building was evaluated, and several deficiencies were expected given that the structure was constructed without strict adherence to the seismic codes, and the following conclusions can be deduced.

1.

The performance of the structure when exposed to Push Y earthquake forces is much better than in the X direction; the maximum roof displacement in this direction is significantly reduced as compared to that in the X direction. This is mostly due to the presence of four shear walls in the direction of the expected in-plane forces, which can undertake the majority of the shear forces as compared to those that take the forces from the X direction. The strong column–weak beam principle comes to mind at this stage. To mitigate this, additional shear walls in the X direction can be installed; this would balance the in-plane forces, improving the structure’s overall resilience.

2.

It is also observed that hinges start forming at the columns, though this should ordinarily start at the beams; these are more significant due to the fear of global progressive collapse, which can be brought about by the failure of columns, as opposed to local collapse, which is common with hinges in beams. This can be addressed by redesigning or retrofitting the structure to shift hinge formations to the beams, adhering to the principles of ductile detailing.

3.

The design lateral loads are much greater than those allowed for the required limit state at the no damage to damage limit state for a hospital. This means that in case of an earthquake action occurring, then there is high potential for the structure to fail. This calls for the concerned parties to take all the necessary measures to minimize the vulnerability of the structure. This necessitates the strengthening of the structure to handle the expected lateral loads effectively.

4.

The structure, with additional shear walls in the Y direction, is structurally non-ductile due to poor seismic rules. This makes it more vulnerable to failure during seismic events, especially in the X direction. This raises concerns about the building’s ability to deliver essential services during seismic occurrences, especially for hospitals.

5.

The evaluation emphasizes the need for retrofitting vulnerable structural elements, particularly columns, to improve seismic performance and reduce collapse risk in non-ductile reinforced concrete frame buildings. However, variability in performance requires careful design and execution considering specific building vulnerabilities. For example, the hospital’s retrofitting measures should focus on improving seismic performance in the X direction, where it currently has significant weaknesses.

6.

From observation, it is evident that the shear walls are improperly located in the structure, leading to torsional irregularity in the building, which contributes to the vulnerabilities observed in the building. This can lead to uneven distribution of forces in the event of an earthquake. Therefore, addressing this issue via the correct placement of shear walls can aid in mitigating seismic risks and enhancing the structure’s resilience.

7.

While pushover analysis offers valuable insights into the seismic behavior of structures, the importance of shear considerations cannot be overstated. Our analysis highlighted potential shear vulnerabilities that warrant further attention and possible retrofitting measures. For future seismic assessments, especially for vital infrastructures, a holistic approach encompassing both flexural and shear behaviors is recommended.