Smart Deployable Scissor Lift Brace to Mitigate Earthquake Risks of Soft-Story Buildings

Abstract

This article introduces a novel smart deployable scissor lift brace system designed to mitigate earthquake risks in buildings prone to the soft-story effect. The system addresses the limitations of traditional retrofitting methods, providing an efficient solution for enhancing the structural integrity of buildings while preserving the functionality of open lower floors, commonly used for car parking or retail spaces. The soft-story effect, characterized by a sudden reduction in lateral stiffness in one or more levels of a building, often leads to catastrophic collapses during large earthquakes, resulting in significant structural damage and loss of life. The proposed system is triggered by signals from the Earthquake Early Warning (EEW) system, advanced technologies capable of detecting and broadcasting earthquake alerts within seconds which are currently implemented in countries and regions such as Japan, parts of the USA, and parts of Europe. The smart deployable system functions by instantly activating upon receiving EEW signals. Unlike traditional retrofitting approaches, such as adding braces or infill walls, which compromise the open layout of lower floors, this innovative device deploys dynamically during seismic events to enhance the building’s stiffness and lateral stability. The article demonstrates the system’s functionality through a conceptual framework supported by proof-of-concept experiments. Historical earthquake time histories are simulated to test its effectiveness. The results reveal that the system significantly improves the stiffness of the structure, reducing displacement responses during events of seismic activity. If properly proportioned and optimized, this system has the potential for widespread commercialization as a seismic risk mitigation solution for buildings vulnerable to the soft-story effect.

1. Introduction

1.1. Brief Review of Earthquake Hazards

Earthquakes are one of the most devastating natural disasters in terms of damage to buildings and human lives. Earthquakes are natural phenomena that have fascinated and terrified humanity throughout history. They result from the sudden release of energy in the Earth’s crust, causing seismic waves to propagate and shake the ground. Mankind has witnessed numerous earthquakes in the past and has faced humongous economic and social losses. Recent large earthquakes in Japan, Haiti, Chile, and New Zealand are excellent examples to illustrate the loss encountered in-terms of human lives due to the collapse of buildings.

Earthquakes themselves do not cause casualties, it is the effects of earthquakes, such as the collapse of buildings, that cause them. According to the US geological survey, in 2019, earthquakes were responsible for an estimated 808,717 deaths in the 21st century, with an average of 42,500 fatalities every year affecting humans between 2000 and 2019. The earthquake of 9.1 magnitude in the Indian Ocean off the coast of Sumatra resulted in a series of large tsunamis which happened in the year 2004 and took 227,899 lives. The magnitude 8.9 Japan earthquake which also resulted in tsunamis in March 2011 was responsible for more than 28,000 deaths; in comparison, the smaller magnitude 7.0 earthquake which occurred in Haiti in January 2010 resulted in an estimated 222,500 fatalities. In recent history, the Pacific Rim is the most affected by seismic activity, with over 80% of the world’s largest earthquakes occurring in this region [1].

1.2. Soft-Story Mechanism

Recent earthquakes have shown that many existing buildings are vulnerable to damage or even collapse during a strong earthquake. Damage and collapse due to the “soft-story effect” are most often observed during and after an earthquake. A soft story refers to a building’s level that exhibits significantly reduced resistance, stiffness, or insufficient ductility (energy absorption capacity) to withstand the stresses induced by an earthquake. Soft-story buildings are characterized by a particular floor that features extensive open space (see Figure 1). Such floors, often, are used as parking garages, large retail areas, or floors with substantial openings.

The design of these buildings introduces a sudden shift in the lateral strength and stiffness along their height, potentially triggering what is known as the “soft-story mechanism”. This occurs when a large lateral force is applied, creating high rotational stress on the outer sections of the ground-level columns. At the same time, the upper structure acts almost like a rigid body, with this imbalance in behavior having the potential to cause, eventually, the entire building to collapse.

Strong earthquakes have caused thousands of injuries, fatalities, and significant economic losses, with building failures often linked to soft/weak story configurations. These structures, particularly vulnerable during seismic events, have been responsible for major damages in past earthquakes, such as the 1995 earthquake in Hyogoken-Nanbu [2], the 1971 earthquake in San Fernando [3], and the 1985 and 2017 Mexico City earthquakes [4,5,6,7]. The Northridge earthquake of 17 January 1994 resulted in a significant level of damage to buildings that had open basements used for parking [8]. In 1997, in Jabalpur, India, the earthquake revealed the handicap of Indian buildings with a soft first story [9]. During the earthquake which occurred on 12 May 2008 in northwestern Sichuan, China, many buildings were significantly damaged, with drifts up to 7.5% (soft-story effect) [10]. The partial collapse of the building “Casa dello Studente” during the earthquake which occurred in L’Aquila, Italy, on 6 April 2009 involved the failure of all columns on the ground floor, attributed to a soft/weak story mechanism [11].

The peculiar behaviour of masonry infill RC frames, in which most of the lateral deformation is concentrated in the open ground story and the upper stories remain vertical and mostly undamaged, was observed in several past earthquakes in India, such as the 2001 Bhuj earthquake [12], the 2004 Great Sumatra earthquake [13,14,15], the 2005 Kashmir earthquake [16], and the 2011 Sikkim earthquake [17,18]. The Lorca, Spain, earthquake of 2011 was a significant event that caused extensive damage to buildings in the area. The seismic activity primarily affected buildings with three to five stories and wide openings on the ground floor, which exhibited a structural vulnerability known as a “soft-story” pattern [19,20]. The 2011 Tohoku Earthquake, which is also referred to as the ‘Great East Japan Earthquake’, was the most powerful earthquake ever recorded in Japan and resulted in the collapse and damage of 45,700 and 144,300 buildings, respectively. Most reinforced concrete buildings that collapsed and were damaged during the earthquake had large openings on the ground story, resulting in weak/soft-story effects [21]. The buildings that experienced the damage during the 2015 Nepal earthquake were found to have either large openings on the ground story or no infill walls, resulting in the plastic hinges experiencing large inter-story drifts [22]. The presence of soft story irregularities was identified as one of the primary factors contributing to the damage of the building in the 2015 Ranau earthquake [23]. In 2022, the Chihshang earthquake, Taiwan, in the southern Hualien and northern Taitung region which had a high seismic intensity, had one notable case which involved the collapse of a three-story residential and commercial mixed-use RC building with a soft-story feature in the downtown area of the Yuli Township, Hualien [24].The recent 2023 Turkey–Syria earthquakes damaged over 100,000 buildings, caused more than 10,000 buildings to collapse, and killed more than 50,000 people. Many soft-story buildings were damaged during this earthquake [25].

Over the decades, retrofitting soft-story buildings to mitigate earthquake effects has focused on the strengthening of the vulnerable first story to improve the overall seismic resilience. Common techniques include the introduction of steel bracing, shear walls, column strengthening, base isolation systems, and the addition of infill walls.

Ferraioli and Lavino [26] proposed a displacement-based design method for the seismic retrofitting of RC buildings using hysteretic dissipative braces which addresses the main issue of the effect of soft-story irregularities and applied it to a real case study of a three-story RC school building in Vibo Valentia, Calabria, Italy, to assess its application potential in current practice.

To create open spaces in buildings, such as parking areas where adding more columns is not feasible, the incorporation of shear walls can be highly beneficial. These walls can resist lateral and shear forces that typically cause significant damage during an earthquake, reducing the need for additional columns [27]. Column strengthening techniques such as FRP jacketing [28,29], steel jacketing [30,31,32], and reinforcement caging have been found to be effective methods for the retrofitting of vulnerable columns and for effectively countering the soft-story mechanism commonly observed in buildings with RC frames. Fakhouri et al. [33] and Briman et al. [34] introduced a novel engineering solution for the seismic isolation of columns that can be utilized to retrofit existing buildings with inadequate soft stories or to construct new structures with soft first stories for architectural or functional purposes. Adding infill walls has been the most practical and affordable way of countering the soft-story effect in buildings. Infill walls function as struts, reducing the lateral load effects on the columns and beams [35].

1.3. Earthquake Early Warning Systems Around the World

In recent years, the Earthquake Early Warning (EEW) system has emerged as a promising technology that attempts to mitigate earthquake risks by providing warning messages to the public and industries. An EEW uses a system of accelerometers, seismometers, communication, computers, and alarms that is devised for notifying adjoining regions of a substantial earthquake while it is in progress. EEW does not predict earthquakes, it can only detect earthquakes and give warnings. EEW consists of the rapid detection of an earthquake that is underway and can make predictions about the expected ground shaking within seconds so that a warning can be broadcast to those in harm’s way. Currently, such systems are implemented in Mexico [36] and Japan [37] and are being tested in other parts of the Americas, Asia, and Europe. The principle behind EEW is based on the fact that a seismic P-wave travels faster (1.73–1.85 times) than the more destructive S-wave [38]. When a P-wave is detected, the approximate location of the epicenter is estimated, and a warning signal is broadcasted to the affected areas before the S-wave arrives. In Japan, EEW provides earthquake warnings in the order of seconds, allowing for the reaction time to mitigate larger earthquake disasters such as shutting down certain industrial operations, reducing train speeds, and evacuating personnel [39]. Figure 2 illustrates the concepts behind an EEW system, schematically.

Damage and collapse due to the soft-story effect are most often observed during and after an earthquake. The traditional methods such as adding infill walls and energy dissipation braces by retrofitting soft-story buildings tend to obstruct the very main purpose of soft stories. These methods of retrofitting soft-story buildings have not proven to be effective at addressing modern-day requirements of open first floors for parking and commercial activities. Keeping in mind the functional requirements of the open first story of buildings, smart devices can be developed which can be deployed instantly during an earthquake using signals provided by the EEW system. At other times, the smart structure can remain in its undeployed state without affecting the functionality of the building. The system can be made to fully deploy automatically and retract itself after each ground motion.

1.4. Novelty of the Proposed Smart Deployable Scissor Lift Brace System

A literature review demonstrated that there has been no attempt to integrate EEW and mechatronic systems to tackle the long-standing problem of the soft-story mechanism. The majority of retrofitting solutions involve the permanent addition of braces that obstruct the original architectural design of the open space at ground level. This article describes the conceptual framework behind and the experimental assessment of a smart deployable scissor lift brace system to mitigate earthquake loading in soft-story buildings. The scissor lift brace system is activated and deployed when an EEW signal is received. Compared to the traditional retrofitting methods, the proposed system has the following advantages.

• It is designed to remain undeployed during regular use, preserving the open space design of the first floor.
• It instantly deploys upon receiving the earthquake signal from the EEW system, thereby enhancing the building’s structural integrity without obstructing its intended use.
• It can be retracted automatically after each seismic event, making the system reusable and ensuring minimum impact on the building’s functionality post-earthquake.

This article presents first the conceptual design, followed by a proof-of-concept experimental investigation. Discussion on the experimental results, requirements for practical implementation, and limitations of the proposed system are also presented.

2. Smart Deployable Scissor Lift Brace

2.1. Conceptual Framework

In the event of an earthquake, the high-frequency compressional P-waves (body waves) which travel fastest are the ones which get detected first by a seismic station. However, the most destructive surface waves (S-waves) travel more slowly and take longer to arrive. It is evident that electromagnetic (300,000 km/s) waves travel at much higher speeds than seismic waves (4–6 km/s) [40]. An EEW system, which consists of the combination of seismometers, sensors, communicators, computers, and alarm systems, uses the same concept to detect and warn of the arrival of seismic waves. It can be used to mitigate the risk of damages and losses in moderately and highly seismically active regions. In the traditional methods to determine the epicentral distance and location, the paramount seismic parameters include the arrival time difference between P-waves and S-waves. Hence, a long time would be required to predict the nature and arrival of an earthquake through these methods [41]. Conversely, EEW systems typically require only a few seconds of P-wave data (0.5–4 s) from two to six stations near the epicenter to detect an earthquake and characterize its location, origin time, and magnitude [42]. This helps provide an initial alert within a few seconds. Although the potential impact of a high-magnitude earthquake can affect a vast area, most of the resulting damage typically occurs within smaller epicentral distances near the fault line that is rupturing. As a result, the primary goal of any EEW system is to swiftly issue an initial alert within a matter of seconds. This urgency ensures that alerts are delivered to areas in close proximity to the epicenter [42]. Subsequent to this initial alert, there is a window of several seconds available for more precise information to be provided or for the alert to be extended to a broader region, particularly in the case of larger seismic events.

In this current investigation, an EEW system is utilized to implement a scissor lift brace mechanism, enhancing the stiffness of the soft-story building during seismic events. Initially, the soft-story building is equipped with an undeployed scissor lift brace, connected to a motor. These components are further linked to the EEW system and internet connectivity. In its undeployed state (Figure 3a), the scissor lift brace mechanism poses no hindrance to the open first story and operates seamlessly under normal conditions without seismic activity.

Upon detection of an earthquake, the EEW system activates the mechanism by transmitting an earthquake alert, prompting the deployment of the scissor lift mechanism (Figure 3b). Prior to the actual seismic event, the mechanism activates a locking mechanism that secures it to the roof of the first story. This proactive measure imparts additional stiffness and strength to the open first story, preventing the formation of plastic hinges and reducing significantly the rotational demand on the structure.

The system operates in an automatic mode, with the scissor lift brace retracting after a certain time has elapsed and restoring the open first story once the earthquake has subsided. This mechanism also serves as a valuable tool for evacuating individuals during an earthquake, with the scissor lift brace ensuring the structural safety of the building until all occupants have been successfully evacuated.

The mechanism relies on electricity as its power source for deployment. Consequently, this system is most effective in buildings with a stable electricity supply and should be deployed, ideally, before the onset of an earthquake to ensure uninterrupted functionality while electric power is still available.

A robust locking mechanism is integrated into this system to ensure secure and proper locking. This feature is crucial to deliver the necessary stiffness and strength precisely when faced with an actual earthquake. A flowchart in Figure 4 shows the sequence of operation steps of the proposed system.

2.2. System Initialization

The structure featuring an open first story is equipped with a scissor lift brace mechanism, positioned at the basement level to accommodate the retracted state of the scissor lift. The mechanism is connected to a threaded bar and a motor, facilitating a rotary action to lift the scissor lift in response to earthquake alerts from the EEW system. A locking mechanism is incorporated into this arrangement to securely fasten the scissor lift to its original structure, ensuring adequate stiffness during an actual seismic event.

In its initial retracted or undeployed state, the system operates without causing disruption to the occupants, allowing the building to maintain its open space. The system’s effectiveness hinges on two essential requirements: a swift deployment speed and a reliable locking system. Achieving a high deployment speed entails the use of a suitable motor and a well-designed mechanical system. Meanwhile, the locking mechanism must be meticulously designed to firmly secure the scissor lift to the original structure, preventing any horizontal movement of the building during an actual seismic event.

2.3. Service Condition

Under service conditions, when there is no ground excitation, the smart scissor lift brace system is connected to the EEW system and waits for a signal. It remains in a state of deployment readiness upon receiving an earthquake signal. Under this service condition, the structure is assumed to be undamaged and linear, with no anticipated relative movement among the base, foundation, and roof.

The shear building model is commonly employed in this scenario, assuming that the floor slabs possess infinite rigidity. This model simplifies the n-level structure into n-degrees of freedom under a one-dimensional vibration. The equation of motion for this system can be expressed as follows:

$$\mathbf{M}\ddot{\mathbf{u}}+\mathbf{C}\dot{\mathbf{u}}+\mathbf{K}\mathbf{u}=-\mathbf{M}\mathsf{\Gamma }\ddot{{\mathbf{u}}_{\mathbf{g}}}$$

(1)

where M and C are n × n mass and damping, respectively, with n being the degree of freedom. K is the stiffness matrix and u is the relative displacement vector. Γ is the influence vector that represents how the ground motion affects the system.

2.4. Activation of the Smart Deployable Scissor Lift Mechanism

Upon receiving a triggering signal from the EEW system, the scissor lift brace initiates deployment and securely anchors to the main building. This action enhances the structure’s stiffness, fortifying it to resist the actual ground shaking. The scissor lift brace system functions as a supplementary structural element, contributing strength to the building. The introduction of these elements alters the engineering characteristics of the structure, mainly adding additional stiffness to the open first story, with the increase in mass and damping due to the additional member being negligible. The modified equation of motion can be expressed as follows.

$$\mathbf{M}\ddot{\mathbf{u}}+\mathbf{C}\dot{\mathbf{u}}+{\mathbf{K}}_{\mathbf{n}\mathbf{e}\mathbf{w}}\mathbf{u}=-\mathbf{M}\mathsf{\Gamma }\ddot{{\mathbf{u}}_{\mathbf{g}}}$$

(2)

where K_new is the modified stiffness matrix which incorporates the increased stiffness from the scissor lift.

$${\mathbf{K}}_{\mathbf{n}\mathbf{e}\mathbf{w}}=\mathbf{K}+{\mathbf{K}}_{\mathbf{s}\mathbf{l}}$$

(3)

where K_sl is the additional stiffness resulting from the scissor lift.

2.5. Post Earthquake Reset

The system possesses an automatic self-reset functionality that comes into use after the cessation of an earthquake. After the ground motion ceases, the scissor lift mechanism resets to its undeployed state. Subsequently, the open ground story can be restored to its original state and utilized for its intended purpose.

2.6. Numerical Example

To illustrate the potential benefits of the proposed deployable scissor lift brace system, a numerical example is presented in this section. A structural plan is presented in Figure 5. The building is a single-story, large open ground floor structure with a steel truss roof. The 1.45 m deep truss roof is made of Australian sections 150UB14 in its top and bottom chords, with web members made of square hollow sections. The roof is supported by 24 columns (200UC46.2). The roof truss has an estimated mass of 85.02 ton. Lateral load resistance is provided by three braced bays in its N–S elevations, and, in its E–W direction, lateral load resistance is provided by moment frame actions. To simplify the analysis, a rigid diaphragm assumption was applied to the roof structure and the structure was analyzed using the structural software Spacegass version 14.2. The following dynamic properties were obtained:

Lateral stiffness (N–S):	99,010.0 kN/m
Lateral stiffness (E–W):	8944.5 kN/m
Fundamental frequency (N–S):	5.29 Hz
Fundamental frequency (E–W):	1.63 Hz

It was observed that the lateral stiffness in the E–W direction was weak due to the absence of braced bays. In a retrofit scenario, a pair of smart deployable scissor lift braces were added to the building’s north and south elevations, as indicted in Figure 5. The scissor lift braces were made up of 150 × 150 × 5 square hollow sections. When deployed, the fundamental frequency in this direction was increased to 3.46 Hz. To compare the structure’s responses under earthquake excitation, a dynamic time-history analysis was conducted with an input ground excitation derived from the 1940 El Centro earthquake in the N–S direction of the structure. Figure 6 presents the roof displacement response. Prior to the retrofit, roof displacement reached 87 mm (story drift equals 1/42). This magnitude of story drift is very likely to cause the soft-story mechanism and a total collapse. If a pair of scissor lift braces were to be installed and triggered by the EEW prior to the arrival of the earthquake excitation, the roof displacement response would decrease to 16.9 mm (story drift equals 1/217).

3. Proof-of-Concept Experimental Investigation

3.1. Experimental Setup and Instrumentation

To demonstrate the feasibility of the proposed system, a proof-of-concept experimental investigation is described herein. Considering the payload capacity of the Quanser Shake Table II, a lightweight single-story structure made of aluminium, bakelite plastic, and steel was fabricated for the experimental investigation. Four columns, consisting of 8 mm diameter galvanized threaded rods, were connected to 10 mm bakelite boards which simulated the floors and roof. The open first floor measured 505 mm × 500 mm × 432 mm (height). Beneath the open first floor, a box made of bakelite boards measuring 505 mm × 500 mm × 100 mm was positioned. The top board of this box included two slits allowing a deployable scissor lift to protrude and attach itself to the roof during deployment. This box also housed other mechanical components and electrical connections, and the box was secured to the shake table. To simulate the weight of the upper floors, steel weight discs were placed on the roof. Each disc weighed 1.5 kg, and five of them were used (total mass of 7.5 kg).

The scissor lift mechanism was constructed using 18 mm × 18 mm × 1.5 mm thick aluminium square tubes connected through pinned joints, designed to fit the height and width of the open ground floor. An 18 mm threaded rod was used to elevate the scissor lift. This actuator was connected to a circular bar with wooden circles at both ends, attached to either side of the scissor lift arrangement. A 12VDC motor was selected to provide the rotary motion for the actuator, enabling the scissor lift to lift itself upon receiving earthquake alerts from the EEW system. A two-piece magnet door stopper was used to lock the scissor lift to the roof of the open first floor, preventing any movement of the scissor lift mechanism during the shaking.

The experimental setup is depicted in Figure 7, Figure 8 and Figure 9. It was secured on a Quanser Shake Table II, which simulated the ground motion in one direction, aligned with the open first floor. Figure 7 shows the structure when the scissor lift brace was completely retracted (i.e., service condition). Figure 8 shows a top view of the box containing the motor, scissor lift brace, and electronics. Figure 9 shows the structures when the scissor lift brace was deployed and attached to the ceiling of the roof.

The responses of the frame were measured independently by two accelerometers (PCB Peizotronics model 603C01, acquired in Melbourne, Australia) positioned at the base (top of the box) and roof levels of the open first floor. The data acquisition (DAQ) device used was a National Instrument NI9234 (acquired in Melbourne, Australia), and the sampling rate used was 1 kHz. In addition, two non-contact laser displacement sensors (Micro-Epsilon model optoNCDT ILR 2250, sourced in Melbourne, Australia), one pointed at the roof and the other pointed at the base of the box measured the displacement during the shaking. Their displacement difference was used as the inter-story drift.

The shake table was controlled via MATLAB SIMULINK (version R2017b), and an algorithm was used to determine the desired position of the shake table, ensuring that the measured accelerations matched the recorded values. Each earthquake history was repeated twice:

• Scissor lift brace undeployed—when the scissor lift was undeployed, the building had an open first floor representing the soft-story effect. Laterally, it was a single-degree-of-freedom system with a fundamental natural frequency of 1.5 Hz determined by the experimental modal analysis.
• Scissor lift brace deployed—when the scissor lift brace was deployed, the open first story gained additional stiffness to mitigate the soft-story effect. The fundamental natural frequency increased to 4.50 Hz when the scissor lift brace was deployed. An increase in the natural frequency of a building generally indicates an increase in stiffness, a reduction in mass, or structural modifications. In this case, as we added an additional support to the original building in the form of a scissor lift, it was evident that the increase in the natural frequency was due to the increased stiffness of the building.

Four historical earthquakes obtained from the PEER ground motion database were simulated. They are listed below and their ground acceleration time histories are shown in Figure 10a, while their corresponding spectra are shown in Figure 10b.

• 1979 Imperial Valley (USGS Station 952)
• 1995 Kobe, Japan (Hik Station)
• 1994 Northridge (CDMG Station 24,514)
• 1992 Cape Mendocino (CDMG Station 89,005)

Figure 10. Input excitations in the experiment, (a) time histories and (b) response spectra.

Figure 10. Input excitations in the experiment, (a) time histories and (b) response spectra.

3.2. Controller, Sensors, and Motor

The required components for this circuit included an Arduino Uno microcontroller and a relay module enabling the control of a high-voltage motor. The motor was powered by a separate 12 V DC supply. The EEW signal was simulated through a local IP address. A diode (e.g., 1N4007) was placed across the relay coil to prevent the back electromotive force (EMF) from damaging the Arduino, while an NPN transistor (e.g., 2N2222) acted as a switch to drive the relay. Resistors were used to limit the current and bias the transistor.

In the circuit, the Arduino sent a control signal to the transistor, which, in turn, drove the relay. A diode was used to protect the system against voltage spikes from the relay’s inductive load. The relay then controlled the motor, with its normally open (NO) terminal connected to the motor and the common (COM) terminal connected to the power supply. The EEWS signal was fed into one of the Arduino’s input pins, and, when the signal was ‘HIGH’, indicating an earthquake, the Arduino activated the relay to power the motor.

When an earthquake was detected, the Arduino sent a ‘HIGH’ signal to the transistor, turning it on and energizing the relay. This closed the relay circuit, powering the motor to drive a scissor lift brace system. Once the EEWS signal returned to ‘LOW’, the Arduino deactivated the relay, turning off the motor. This setup allowed for an automated response to the seismic activity. A circuit diagram is shown in Figure 11.

3.3. System Initialization and Activation

During the system initialization stage, the scissor lift brace mechanism, along with other mechanical components, remained in its retracted or undeployed state, housed within a box located at the bottom of the open first floor. In this undeployed state, the scissor lift mechanism did not disrupt the occupants and maintained the building’s open architectural plan. Once the system entered the service mode, the microcontroller continuously updated its status with the EEW system and anticipated an earthquake signal.

In the experiment, upon receiving a signal from the EEW via an ethernet shield, the scissor lift brace system became activated. The scissor lift brace took 14.1 s to deploy completely and anchor to the main building.

3.4. Experimental Results

A total of eight earthquake simulations were conducted, and the test setup proved to be robust and repeatable. The re-centering mechanism was performed successfully after each ground motion had ceased. The acceleration responses of the structure, with and without the smart scissor lift brace, are presented in Figure 12. Peak values of the structural responses (absolute accelerations) are compared in Figure 13. It is evident that the roof accelerations generally increased with the exception of the Kobe Eerthquake. When the scissor lift brace was deployed, additional stiffness was added to the structure, causing an increase in vibration. An increase in the roof vibrational level is an adverse effect; however, it is an inevitable result to control inter-story displacement as discussed below.

On the other hand, the inter-story drifts were measured using the difference in displacement between the roof and the base of the open floor. The time-history response of the inter-story drifts are shown in Figure 14. The reduction in the inter-story drift is summarized in

Table 1. Comparison of the inter-story drifts: with and without the smart scissor lift system.

Earthquake	Scissor Lift Undeployed (mm)	Scissor Lift Deployed (mm)	% Reduction
1979 Imperial Valley	4.44	0.77	83%
1995 Kobe	4.93	0.35	93%
1992 Mendocino	4.79	0.84	82%
1994 Northridge	5.00	1.05	79%

. There was a significant reduction in the inter-story drift when the open first floor of the building was equipped with the smart scissor lift system for all four earthquake events. This is a more favourable condition for the soft-story building, as the decrease in the inter-story drift indicates less deformation and improved building resilience during an earthquake.

4. Discussion

The experimental results in Section 3 show the feasibility of the proposed smart deployable scissor lift brace system. The requirements for practical implementations and its limitations are discussed below.

4.1. Requirements for Practical Implementation

• Power supply—In the event of an earthquake, the electricity supply may be interrupted. To ensure the system’s functionalities during and after an earthquake event, an uninterruptible power supply (UPS) must be installed.
• The timing of deployment—the timing of the deployment of the structure and being able to securely anchor it to the main building is critical. There must be a sufficient time interval from the deployment of the structure to its secure attachment to the main building and the arrival of the earthquake. The deployable structure and actuators should be engineered to ensure optimal performance even in close proximity to the earthquake’s epicenter, where the warning time may be very short.
• Anchoring system—the anchoring system must be robust enough to firmly hold the deployed structure in place during an earthquake, preventing excessive acceleration of the roof that could lead to detrimental resonance throughout the system.
• The obstruction of the deployable mechanism must be prevented during the normal usage of the ground level. The space required for the deployment needs to be fenced off from the occupants to prevent potential harm.
• Earthquake signals and fail-safe design—as the system only relies upon the signals from the EEW system, there should be a substitute when the signal from the EEW system fails, such as onsite accelerometers or manual excitation. The other issue is sensitivity. High sensitivity may cause unnecessary triggering and the users may become troubled. There should be a fail-safe system developed to differentiate between an actual earthquake signal and a vibration due to the traffic or the wind.
• Damping element—additional damping elements such as fluid dampers could be added to the proposed scissor lift mechanism to improve its vibrational control. However, this will result in the additional complexity of the anchorage design, which is envisaged to be further researched. Recent developments in self-centering devices [43,44] may further enhance the system’s performance and requires further research.
• Cybersecurity—since the proposed system requires an internet connection between the EEW and the deployable structure, there may be network security issues. In future developments, encryption and decryption techniques could be used to ensure the correctness of the signals, or a separate network connection could be established between the building and the EEW system.

4.2. Implications for the Structural Design

The proposed system best suits the retrofit scenario where the existing structure is to be kept, and the usage of an open ground floor is required for architectural or functional purposes. It should be noted that the scissor lift brace members must remain elastic under earthquake conditions, including sufficient resistance to buckling phenomena. Inelastic deformation or buckling jeopardizes the scissor lift braces’ movements. Furthermore, if the soft-story mechanism is expected in more than one direction, an additional set of scissor lift braces will be required.

4.3. Limitations of the Proposed System

As in all engineering systems, there are limitations, and they must be considered. They include:

• The proposed system will only work in regions where an EEW is available, such as Japan, parts of the USA, Mexico, and Europe. Also, if the EEW is unable to provide a warning signal, the proposed system will not function.
• If the epicenter happens to be in close proximity to the structure, there will be insufficient time for the deployment of the scissor lift brace.
• A certain amount of excavation is needed to house the mechanical system in the ground in retrofit scenarios.
• The proposed system confers lateral stiffness to the structure; such an increase must be analyzed and the subsequent increase in the base shear must be tolerated.

5. Conclusions

The soft-story mechanism is a long-standing problem affecting many existing buildings where the ground level has a much smaller lateral stiffness compared to that of the rest of the building. There has been no attempt in the literature to utilize the newly developed Earthquake Early Warning (EEW) system to solve this problem. This paper presents a novel EEW-activated deployable scissor lift system specifically aimed at solving such a problem. When no earthquake is detected, the scissor lift brace system remains retracted in the basement of the building, preserving the building’s open floor plan without causing any obstructions. The system features an onboard microcontroller that continuously awaits the signal from the EEW. Upon receiving a signal, indicating imminent ground motion, the scissor lift brace deploys and anchors itself to the ceiling of the ground level, enhancing its lateral stiffness and strength to withstand strong earthquake forces. Once the ground motion ceases, the deployed system is retracted, returning to its initial state. This process is fully automated and repeatable. The proposed system provides an alternative retrofit solution to soft-story buildings. It retains the intended open ground level which the traditional means of strengthening, such as the addition of permanent braces, are unable to do.

In a proof-of-concept laboratory experiment, a single-degree-of-freedom test model was fabricated. The model was equipped with a communication module and a microcontroller to deploy a scissor lift brace. Actuation was delivered by a DC motor through a threaded shaft. A simulated EEW signal triggered its deployment. The Quanser Shake Table II was utilized to simulate ground vibrations. The parameters from four historical earthquakes were used as input excitations. A single-story test model was tested when the (1) scissor lift brace system was in its undeployed state and when the (2) EEW triggered the deployment of the scissor lift brace. The results demonstrate that there was an increase in the vibrational responses at the roof level but also a significant decrease in inter-story drifts (79–93% reduction) when the brace was deployed.

The proposed system is suitable for buildings which suffer from the soft story mechanism, where excessive deflection is expected at the ground level due to low lateral stiffness. The experimental results show that a significant reduction in the inter-story drift was achieved when the scissor lift brace system was deployed. It signifies improved structural performance, reduced risk of catastrophic failure, enhanced safety for the occupants, and an increased overall resilience. This is a crucial measure of the effectiveness of any retrofitting or strengthening measures applied to such buildings.

Several issues related to the full-scale implementation of this system are also discussed, including the system’s physical and electrical requirements, cybersecurity concerns, and the need for a fail-safe activation mechanism. These factors are important for potential integration with the Internet of Things (IoT) concept. The implications for future structural retrofits are discussed, and the limitations of the proposed system are also discussed in the article.