Critical response of reinforced concrete moment-resisting frames with steel damper columns subjected to sequences of two pulse-like ground motions

Abstract

A reinforced concrete (RC) moment-resisting frame (MRF) with steel damper columns (SDCs) can be considered a damage-tolerant structure. The behavior of such a structure depends on the strength balance of the RC MRF and SDCs, and the pinching behavior of RC members. In this article, the seismic behavior of an RC MRF with SDCs under pulse-like ground motion sequences is investigated by applying an extended incremental critical pseudo-multi-impulse analysis (ICPMIA). This article consists of two analytical studies. The first analytical study focuses on (a) the degradation in energy dissipation of an RC MRF with SDCs and (b) the increase in response period due to prior earthquake damage. An extended ICPMIA of RC MRF models is carried out. The second study focuses on the influence of the pulse period of pulse-like ground motion sequences on the response of RC MRFs with SDCs. The main findings are as follows. (1) When the pulse velocities of the two multi impulses (MIs) are the same in sequential MIs, the peak displacement is larger than that of a single MI if the first and second MI have the same sign. This trend is notable when the SDC strength is relatively low, and the pinching behavior of RC beam is significant. (2) The degradation in energy dissipation of an RC MRF in the second input is notable when the pinching behavior of RC beams is significant and the SDC strength is relatively low, whereas such degradation is limited when the SDC strength is relatively high. (3) The increase in RC MRF response period in the second input is notable when the pinching behavior of RC beam is significant. (4) For nonlinear time history analysis (NTHA) using sequential ground pulses, the most critical period of the second pulse is longer than that of a single pulse. (5) The most critical response obtained from NTHA for the pulses in (4) can be approximated by the extended ICPMIA results.

1 Introduction

1.1 Background and motivations

Strong earthquakes, which cause moderate to severe damage to building structures, often occur as a series of earthquake sequences, not as a single event. In past major seismic events such as the 2011 off the Pacific coast of Tohoku Earthquake in Japan, the 2016 Kumamoto Earthquake in Japan, and the 2023 Kaharamanmaraş Earthquake in Turkey, strong aftershocks occurred following the mainshock, forming foreshock–mainshock sequences. In addition, a pair of seismic events closely spaced in time and location (doublet earthquakes) occurred in northwest Iran in August 2012 (Yaghmaei-Sabegh, 2014). Therefore, the nonlinear response of a building structure subjected to an earthquake sequence is important. It is very important to mention that the interval between two severe seismic events (e.g., the mainshock and the major aftershock) may be very short (a few hours or a few days). Therefore, the restoration of damaged structural members cannot be completed before the next strong seismic event. In a reinforced concrete (RC) moment-resisting frame (MRF), the cracking of concrete, yielding of reinforcement, and deterioration of concrete-steel bonding will cause the stiffness and strength degrading. Such degradation causes an increase in the natural period and deterioration in energy dissipation capacity of the whole structure. Therefore, the nonlinear characteristics of a damaged RC MRF are different from those of a non-damaged one.

This study focuses on the nonlinear behavior of an RC MRF with SDCs under a pulse-like ground motion sequence.

The responses of structures under pulse-like ground motions have been widely investigated, especially after the 1994 Northridge and 1995 Kobe earthquakes. Alavi and Krawinkler (2000) and Alavi and Krawinkler (2004) investigated the response of generalized steel MRF models using a rectangular-pulse wave model. Mavroeidis et al. (2004) investigated the response of elastic and inelastic single-degree-of-freedom (SDOF) systems subjected to near-fault ground motions using the velocity pulse model proposed in their previous study (Mavroeidis and Papageorgiou, 2003). They pointed out that using the pulse period () and amplitude () “effectively normalized the elastic and inelastic response spectra of SDOF systems subjected to actual near-fault records.” Xu et al. (2007) considered the response of an SDOF model with nonlinear viscous and hysteretic dampers subjected to the velocity pulse model. According to the analysis of near-fault ground motion records, Baker (2007) proposed a method to extract the largest velocity pulse from a given recorded ground motions. Then, Shahi and Baker (2014) extended this method for the multicomponent ground motions. They also pointed out that the pulse period () becomes longer when the moment magnitude of the event () is large, which is consistent with the results by Mavroeidis and Papageorgiou (2003).

These studies emphasized that the ratio of the pulse period () to the fundamental structure period () is a key parameter for the response of a building subject to pulse-like ground motions. As mentioned above, the fundamental period of a damaged RC structure becomes longer owing to the damage caused by previous seismic events. Therefore, the relation between the pulse period and the fundamental period of a damaged RC structure is important for studying the response of such a structure to an earthquake sequence.

The nonlinear response of building structures subjected to seismic sequences has been studied by many researchers (e.g., Mahin, 1980; Amadio et al., 2003; Hatzigeorgiou and Beskos, 2009; Hatzigeorgiou and Liolios, 2010; Ruiz-García and Negrete-Manriquez, 2011). After the 2011 off the Pacific coast of Tohoku Earthquake in Japan, the number of studies has been increasing (e.g., Ruiz-García, 2012; Di Sarno, 2013; Ruiz-García, 2013; Abdelnaby, and Elnashai, 2014; Yaghmaei-Sabegh and Ruiz-García, 2016; Abdelnaby, 2016; Di Sarno and Amiri, 2019; Yang et al., 2019). Some of them used as-recorded earthquake sequences as the seismic input for NTHA (e.g., Mahin, 1980; Hatzigeorgiou and Liolios, 2010; Ruiz-García and Negrete-Manriquez, 2011; Abdelnaby, and Elnashai, 2014; Abdelnaby, 2016), while the others used artificial earthquake sequences. To model earthquake sequences, repeated approach (applying the same ground motion several times) has been applied by Amadio et al. (2003), Hatzigeorgiou and Beskos (2009). While in the other studies, randomized approach (applying the ground motion sequences from the randomly chosen ground acceleration) have been applied for the analysis, as an alternative of repeated approach (e.g., Hatzigeorgiou, 2010a; Hatzigeorgiou, 2010b; Hatzigeorgiou and Liolios, 2010). Ruiz-García and Negrete-Manriquez (2011) pointed out that the repeated approach would not be suitable to model the ground motion sequences, because the frequency characteristics of recorded aftershock are weakly corelated with that of mainshock. In addition, they concluded that “as-recorded aftershocks do not significantly increase peak and permanent drift of existing steel frames”, unlike the artificial seismic sequences (repeated approach). Similarly, Yaghmaei-Sabegh and Ruiz-García (2016) pointed out that, from the analysis results of doublet earthquakes that occurred in northwest Iran in August 2012, the frequency characteristics of the second recorded mainshock in doublet earthquake is different from that corresponding to the first recorded mainshock.

One of the reasons for applying the repeated approach to model the seismic sequences is to avoid the complexity of ground motion characteristics, as mentioned by Amadio et al. (2003). Applying the real ground motion sequences or artificial ground motion sequences following randomized approaches would be more complex to understand the nonlinear response of structures under earthquake sequences. However, because the frequency characteristics of the second earthquake (the recorded aftershock in case of mainshock-aftershock sequences) is different from that corresponding to the first recorded earthquake (mainshock), the repeated approach is not considered as the proper modeling of earthquake sequences for NTHA.

Since 1980’s, the concept of “energy balance” has been applied in the study of the nonlinear response of structures (e.g., Akiyama, 1985; Akiyama, 1999; Uang and Bertero, 1990). Recent advances in energy-based seismic engineering can be found in the literature (Benavent-Climent and Mollaioli, 2021; Varum et al., 2023; Dindar et al., 2025). Akiyama (1985) has proposed the equivalent velocity of the total input energy () as the seismic intensity parameter related to the cumulative response of structures. While, for the prediction of the nonlinear peak response of ductile RC structures, Inoue and his research group proposed the equivalent velocity of the maximum momentary input energy () as the seismic intensity parameter (Hori et al., 2000; Inoue et al., 2000; Hori and Inoue, 2002). They showed in Hori et al. (2000) that “momentary input energy is related to response displacement of structures immediately, and that energy input process is important for the evaluation of the damaging properties of earthquakes such as impulsive or cyclic.” Following their study, the author (Fujii et al., 2021) formulated the “time-varying function” for calculating the momentary input energy from the complex Fourier spectrum of ground acceleration. In addition, the momentary input energy and total input energy are implemented to a simplified procedure for predicting the peak and cumulative response of an RC MRF with SDCs (Fujii and Shioda, 2023).

There are also several studies of the nonlinear response of building structures subjected to earthquake sequences in terms of energy (e.g., Zhai et al., 2016; Alıcı and Sucuoğlu, 2024; Donaire-Ávila et al., 2024; Galé-Lamuela et al., 2025). Specifically, Donaire-Ávila et al. (2024) and Galé-Lamuela et al. (2025) examined the applicability of Akiyama’s cumulative energy distribution theory (Akiyama, 1985; Akiyama, 1999) in case of RC building models subjected to earthquake sequences. They noted that “the distribution of the cumulative dissipated energy among the stories remained basically the same across all events within a sequence, regardless of the design approach or the proneness of the frame to damage concentration.”

Takewaki and his group have developed an innovative energy approach (Kojima and Takewaki, 2015a; 2015b; 2015c; Akehashi and Takewaki, 2021; Akehashi and Takewaki, 2022a; Akehashi and Takewaki, 2022b). They developed a simplified seismic input model by using a series of impulses for calculation on the critical earthquake response of structures, named as critical double impulses (DI) and critical multi impulse (MI). The development of this theory and recent achievements are summarized in the literature (Takewaki and Kojima, 2021; Takewaki, 2025). Following their studies, this author has applied their pseudo-multi impulses (PDI) and pseudo-multi impulse (PMI) analyses to an RC MRF with SDCs (Fujii, 2024a; 2024b) to verify a simplified procedure for predicting the peak and cumulative response of an RC MRF with SDCs (Fujii and Shioda, 2023). Then, the author proposed an extended version of incremental critical PMI analysis (extended ICPMIA) for predicting the nonlinear response of structures subjected to earthquake sequences (Fujii, 2025a).

In the author’s view, the strong points of this extended ICPMIA are i) it can be performed if the structural model is stable for NTHA; ii) it automatically calculates the cumulative response of members, which is important for discussing the accumulated damages of the structure under earthquake sequences; iii) the responses obtained from it can be easily associated with ground motion using an energy spectrum as demonstrated in a previous study (Fujii, 2025a); and iv) its results make nonlinear structural characteristics much easier to understand because the seismic input is simplified. In the extended ICPMIA, the simplification of seismic input introduced in the original PMI is still valid. The nonlinear characteristics of the structure obtained from the extended ICPMIA are independent of the complex frequency characteristics of selected input ground motion sequences. This is because the frequency characteristics of input ground motion are automatically determined from the nonlinear characteristics of the structure itself. This is why the extended ICMPIA would be a powerful tool for understanding the basic behavior of structures subjected to a sequential seismic input.

1.2 Objectives

The second study focuses on the influence of the pulse period of pulse-like ground motion sequences on the response of RC MRFs with SDCs. An NTHA of RC MRF models with SDCs is carried out using a model of sequential pulse-like ground motion. In this analysis, the pulse periods of the first and second inputs are different, whereas the peak velocities of the first and second inputs are the same. The second analytical study addresses the following two questions:

The remainder of this article is organized as follows. Section 2 outlines the extended ICPMIA. Section 3 presents an RC MRF building model with SDCs. Section 4 shows the ICPMIA results for this building model and then discusses i) the relationship between the equivalent velocity of the maximum momentary input energy of the first modal response () and the maximum equivalent displacement of the first modal response (), ii) the response period of the first mode (), and iii) the hysteretic dissipated energies of RC MRFs and SDCs ( and , respectively) during the first and second MIs. Then, NTHAs of RC MRFs with SDCs are carried out using models of pulse-like ground motion, and those results are compared with those of the extended critical PMI analysis in Section 5. Conclusions and further directions of this work are discussed in Section 6.

2 Outline of the extended ICPMIA

2.1 Extended critical PMI analysis

Figure 1 outlines the extended critical PMI analysis considering sequential input. Detailed formulations of the extend critical PMI analysis can be found in the previous study (Fujii, 2025a).

FIGURE 1

Fujii (2025a): c4 and c5 are newly added to show the time-history of strain energy of RC members and SDCs.

A planar frame building model (with stories) is subjected to a pseudo-impulsive lateral force proportional to the first mode vector (), as shown in Figures 1a,b. In this figure, is the ground motion velocity increment, and are respectively the equivalent displacement and the equivalent velocity increment of the equivalent SDOF model representing the first modal response of building model, is the velocity increment vector of the building model.

In the extended critical PMI analysis, the seismic input is modeled as the sequences of two MIs as shown in Figure 1c1: in this figure, is the number of the pseudo-impulsive lateral force in the -th MI ( = 1, 2), is the interval length between the first and second MI, is the pulse velocity in the -th MI, _j is the time when the -th pseudo-impulsive lateral force acts through the -th MI. Note that the intensity of the first and last ground motion velocity increments in each MI is the half of the pulse velocity () in case of is larger than 3, following the study by Kojima and Takewaki (2015c).

The time-history of the equivalent displacement is shown in Figure 1c2. In Figure 1c2, the peak equivalent displacement during the -th MI (_j) is obtained via Equation 1:

In Equation 1, _j is the time at the -th local peak of during the -th MI, as shown in Figure 1c2. The peak equivalent displacement of the first modal response over the course of the entire sequential input () is obtained via Equation 2:

The time-history of the energy of the first modal response (the kinetic energy , the damping dissipated energy , the cumulative strain energy , and the cumulative input energy ) is shown in Figure 1c3. The maximum momentary input energy of the first modal response per unit mass during the -th MI () can be obtained via Equation 3:

In Equation 3, is the momentary input energy of the first modal response per unit mass at time = _j during the -th MI. The equivalent velocity of the maximum momentary input energy of the first modal response during the -th MI () is defined in Equation 4:

Therefore, the equivalent velocity of the maximum momentary input energy over the course of the entire sequential input () is obtained via Equation 5:

Next, the response period of the first mode during the -th MI () is defined as follows. When occurs at time = , the response period is calculated as twice the interval between the two local peaks in Equation 6:

For the case in Figure 1c, the red curve shown in the time history of the equivalent displacement () indicates the half cycle of the structural response when occurs. Therefore, because = = 3 in this case, the response period of the first mode during the first and second MIs (₁ and ₂, respectively) is calculated as

The cumulative input energy of the first modal response per unit mass during the -th MI () can be obtained via Equation 7:

The equivalent velocity of the cumulative input energy of the first modal response during the -th MI () is defined in Equation 8:

Therefore, the equivalent velocity of the cumulative input energy over the entire sequential input () is obtained via Equation 9:

Next, the cumulative energies of RC members and SDCs at time ( and , respectively) are defined as follows. The time-histories of these cumulative energy are shown in Figures 1c4,c5. The cumulative strain energy of the whole structure at time is defined in Equation 10:

In Equation 10, and are the restoring force and velocity vector of the -story building model. Then and are calculated via Equations 11,12, respectively:

In Equation 12, is the cumulative strain energy of the damper panel of each SDC in the -th story; and , , and are the shear force, shear strain, and height of the damper panel of each SDC in the -th story, respectively.

In this study, the cumulative energies of RC members and SDCs during the first MI ( and , respectively) and the second MI ( and , respectively) are discussed. These cumulative strain energies are calculated via Equation 13:where and are the cumulative strain energies of RC members and SDCs just before the second MI starts, and is the ending time of the analysis.

2.2 Procedure for the extended ICPMIA

3 Building model

The building models analyzed in this study were three eight-story housing buildings shown in Figure 2. The structural plans of the three models (Dp033, Dp050, and Dp100) are shown in Figures 2a–c. Model Dp100 in Figure 2c was the same model used in a previous study (Fujii, 2025a), while models Dp033 and Dp050 in Figures 2a,b had one-third and one-half the number of SDCs as Dp100, respectively. As mentioned in the previous study (Fujii, 2025a), model Dp100 was designed using simplified procedure by Mukoyama et al. (2021): the displacement limit was assumed to be 1/75 of the equivalent height (= 0.232 m), while the design earthquake spectrum was the code-specific spectrum [soil condition; type-2 (normal)] of the Building Standard Law of Japan (Building Center of Japan, 2016). The unit weight per floor mass was assumed to be 13 kN/m², which is the typical value of the Japanese RC housing building. Frames A and B of all three models were assumed to extend infinitely in both longitudinal directions, and the colored area in Figures 2a–c was modeled for the analysis. Detail of the building model properties are given in Supplementary Appendix S1. To check the strength balance of the RC MRF and SDCs, the ratio of the initial yield strength of the SDCs in the -th story () to the yield strength of the RC MRF in the -th story (), , was calculated for each model. The ranges of the ratio of models Dp033, Dp050, and Dp100 were 0.079 to 0.109, 0.119 to 0.164, and 0.238 to 0.327, respectively.

FIGURE 2

In the structural modeling, only planar behavior in the longitudinal direction was considered. All frames were connected through a rigid slab. Figure 2d shows the structure of Frame A in model Dp050. Only a two-span area was extracted from the endless longitudinal frames in Dp050; therefore, the end of each boundary RC beam was supported by a horizontal roller. Figure 2e shows the structural model of Frame A in Dp100. This used the same modeling scheme as in a previous study (Fujii, 2025a). Similar modeling schemes were applied to model Dp033. The natural periods of the first modal responses in the elastic ranges of models Dp033, Dp050, and Dp100 were 0.542, 0.520, and 0.459 s, respectively.

To investigate the influence of the pinching behavior of RC beams to the nonlinear behavior of RC MRF with SDCs, two cases are considered in the hysteresis rules for RC beams in this study. Figure 3a shows the hysteresis rule of RC beams with significant pinching behavior, while the hysteresis rule shown in Figure 3b is the rule of RC beams with no pinching. Note that the same hysteresis rules applied in a previous study (Fujii, 2025a) are applied in this study. To control the pinching behavior of RC beams, the parameter was set to 0.25 in case of significant pinching, while was set to 1.00 in case of no pinching. No pinching behavior is considered in RC columns in this study. Therefore, the hysteresis rule shown in Figure 3b ( = 1.00) is applied for RC columns, regardless of the hysteresis model applied in RC beams. The detail of the hysteresis rule of RC members can be found in Supplementary Appendix S2. The trilinear hysteresis model considering strain hardening of the low-yield-steel damper panel (Ono and Kaneko, 2001) shown in Figure 3c is applied for the SDC damper panel. The damping matrix was assumed to be proportional to the instantaneous (tangent) stiffness without an SDC. The damping ratio of the first modal response in the elastic range of the model without an SDC was assumed to be 0.03. Second-order effects were neglected in this analysis.

FIGURE 3

Fujii, 2025a). (a) RC beam (c = 0.25), (b) RC beam (c = 1.00) and RC column, (c) damper panel (SDC).

4 ICPMIA of the building model

The analytical study in this section focused on (a) the degradation in energy dissipation of an RC MRF with SDCs and (b) the increase in the response period due to prior earthquake damage.

4.1 Analysis method

First, an ICPMIA considering a single MI was carried out: the numbers and were set as = 4 and = 0. The value of was set initially at 0.1 m/s with increments of 0.05 m/s until reached 150% of the target displacement (). Then, the value of that corresponded to was found by linear interpolation. In this analysis, was set to be 1/75 of the equivalent height (= 0.232 m), because this is the design limit assumed in the seismic design of model Dp100 in a previous study (Fujii, 2025a). Note that when reached 0.232 m, some of the RC beams and the bottom of the columns in the first story yielded, following the yielding of SDC damper panels. Therefore, the damage level of the whole model could be considered “moderate” when reached 0.232 m.

Next, an extended ICPMIA considering sequential MIs was carried out: the numbers and were set as = = 4. The value of was set as the value corresponding to , while the value of was set initially at 0.1 m/s with increments of 0.05 m/s until reached 150% of . As in a previous study (Fujii, 2025a), were set to 64 and 65. The case = 64, when the first and second MIs had opposite signs, is referred to as “Sequential-1”, while the case = 65, when the first and second MIs had the same sign, is referred to as “Sequential-2”. The ending time () was determined as the ending time of the 64th half cycle of free vibration after the action of the -th pseudo-impulsive lateral force.

A previous study by the author (Fujii, 2025b) investigated the suitable for near-fault earthquake ground motion using the velocity pulse model by Mavroeidis and Papageorgiou (2003). It concluded that the most suitable for the velocity pulse model analyzed was 4. Therefore, was set to 4 in this study.

4.2 Analysis results

4.2.1 Single MI

FIGURE 4

In the following analysis, the value of was set to the value in Figure 4.

4.2.2 Sequential MIs (₂V_p = ₁V_p)

Next, the extended ICPMIA results for = are presented. Figure 5 shows comparisons of the local response in each model in terms of the peak story drift () and the normalized cumulative strain energy of the SDC damper panel (), given by Equation 14:

FIGURE 5

Figure 6 shows the hysteresis loops from PMI analysis for = in Dp033 ( = 0.25) and Dp100 ( = 0.25). The red curve indicates the half of the structural response when occurred. This figure also shows the value of and in each MI. In addition, ₁ is the ending time of the interval between the first and second MIs (=₂), and ₂ is the ending time of the free vibration after the second MI (= ). Therefore, the points ₁ and ₂ in this figure indicate the residual equivalent displacement after each input is finished.

FIGURE 6

4.2.3 Sequential MIs (₂V_p ≠ ₁V_p)

Next, the extended ICPMIA results are shown for the case when is fixed while increases until reaches 150% of .

In Figure 7, the – curves of the second MI obtained from Sequential-1 and 2 (green and red curves, respectively) are compared with the – curve for a single MI (blue curve). In addition, large colored plots indicate the responses in the first and second MIs when equals , which is the value in Figure 4.

FIGURE 7

FIGURE 8

FIGURE 9

FIGURE 10

4.3 Summary of results and discussion

Therefore, the cumulative strain energy demand of SDCs would be more pronounced in earthquake sequences. This is due to the decrease in energy dissipation in the second seismic input of RC members, not only the increase in seismic energy input. This would be pronounced when significant pinching of RC members was expected and the SDC strength was relatively low.

As far as the results discussed herein is considered, the increase of peak response in the sequential MIs was minimal in model Dp100: in this model, the range of the ratio was 0.238 to 0.327. However, the increase of peak response is non-negligible, even in model Dp100. Therefore, the ratio may need to be larger than that in model Dp100, to minimize the increase of peak response in earthquake sequences.

5 Responses of building models under sequential pulse-like ground motions

The analytical study in this section focused on the influence of the pulse period of pulse-like ground motion sequences on the responses of RC MRF models.

5.1 Analysis method

5.1.1 Pulse-like ground motion models

Figure 11 shows the pulse-like ground motion models used in NTHAs. In this study, the velocity pulse model proposed by Mavroeidis and Papageorgiou (2003) was used as the single seismic input. The time history of the velocity pulse of this model is expressed as Equation 15:where is the velocity amplitude; is the pulse period; and , , and are the parameters of this pulse model. Here, the parameters were set as = 10 s, = 2, and = 0° and 90°. The single-pulse model = 0° is referred to as Single-Pulse-000, while = 90° is referred to as Single-Pulse-090. Acceleration time histories of these single-pulse models ( = 1.0 m/s, = 1.0 s) are shown in Figure 11a.

FIGURE 11

Figure 11b shows the energy spectra ( and ) of these single-pulse models ( = 1.0 m/s, = 1.0 s). The and spectra were calculated using the time-varying function proposed in one of our previous studies (Fujii et al., 2021): the complex damping coefficient was set to 0.10, following another of our previous studies (Fujii and Shioda, 2023). The amplitude of each single-pulse model was determined by equating the peak value of the spectrum in Figure 11b and the value corresponding to in Figure 4.

The sequential-pulse model used in this analysis was based on the velocity pulse model by Mavroeidis and Papageorgiou (2003). The time history of the sequential velocity pulse model is expressed as Equation 16:where and are the amplitude and pulse period of the -th input ( = 1, 2); and , , and are the parameters of this pulse model. In this analysis, the parameters were set as = 10 s, = 30 s, = = 2, and = = 0° and = = 90°. The sequential-pulse model = = 0° is referred to as Sequential-Pulse-000, while = = 90° is referred to as Sequential-Pulse-090. Acceleration time histories ( = = 1.0 m/s) are shown in Figure 11c1 for Sequential-Pulse-000 ( = 1.1 s, = 1.5 s) and Figure 11c2 for Sequential-Pulse-090 ( = 1.2 s, = 1.7 s). This section also studies the influence of the signs of the first and second inputs, namely, the same-sign case = and opposite-sign case = .

5.1.2 Analysis procedure

Note that different values of could be obtained for Single-Pulse-000 and Single-Pulse-090.

5.2 Analysis results

5.2.1 Single-pulse model

Figure 12 shows comparisons of the local responses ( and ) obtained from the NTHA using the single-pulse models and critical PMI analysis. This figure shows all the NTHA results for Single-Pulse-000 and Single-Pulse-090 and their envelopes. “PMI” in this figure is the ICPMIA result corresponding to in Figure 5.

FIGURE 12

Therefore, the and envelopes from NTHA for both Single-Pulse-000 and Single-Pulse-090 can be approximated by the ICPMIA results, assuming = 4. This result is consistent with the results of a previous study (Fujii, 2025b).

Figure 13 shows comparisons of the – relationship obtained from NTHA in the single-pulse models. In this figure, the ICPMIA values of and are shown for comparison.

FIGURE 13

5.2.2 Sequential-pulse model

Figure 14 shows comparisons of the local responses ( and ) obtained from NTHA using sequential-pulse models and extended critical PMI analysis. This figure shows all the NTHA results for Sequential-Pulse-000 and Sequential-Pulse-090 along with their envelopes. “Extended PMI” in this figure consists of the envelopes of Sequential-1 and 2 in Figure 5.

FIGURE 14

Figure 15 shows comparisons of the – relationship from NTHA in the sequential pulse models. For each value, the larger value obtained from NTHA using the same-sign ( = ) and opposite-sign ( = ) inputs is plotted in this figure. The values of and obtained from extended ICPMIA (Sequential-2) are shown for comparison.

FIGURE 15

5.3 Discussion

The second conclusion is consistent with the results in the previous section. That is, because the response period of the first mode in the second MI () is longer than that in the first MI(), should be longer than to produce the most critical response for a sequential input of two pulses. It should be emphasized that applying the same ground acceleration several times (the repeated approach), which has been done in many past studies, does not produce the most critical response for the earthquake sequences.

6 Conclusion

The second analytical study focused on the influence of the pulse period of pulse-like ground motion sequences on the response of RC MRFs with SDCs. An NTHA of RC MRF models with SDCs was carried out using the sequential pulse-like ground motion model. The main conclusions from the second part can be summarized as follows:

Conclusions I) to V) answer questions I) to V) in Section 1.2. These conclusions support the effectiveness of the extended ICPMIA presented in the author’s previous study (Fujii, 2025a).

The significance of this study can be summarized in two points. The first is that the extended ICPMIA clearly evaluates the basic behavior of RC MRFs with SDCs subjected to an earthquake sequence. Specifically, this study has clearly evaluated the influence of the strength ratio of SDCs to RC MRF and the pinching behavior of RC beam on (a) the peak displacement of the RC MRF in a sequential seismic input, (b) degradation in hysteretic dissipated energy of RC members and SDCs during the second seismic input in the non-damaged case, and (c) the increase in natural period in the second seismic input in the non-damaged case. Unlike the results of most previous studies, the results herein are independent of the complex frequency characteristics of the selected input ground motions used in NTHA. Therefore, those presented herein represent the basic nonlinear characteristics of an RC MRF with SDCs because they are derived from the analyzed structures themselves. The second point is that the most critical response of an RC MRF with SDCs subjected to a sequential pulsive input can be approximated by the extended ICPMIA. This achievement contributes to the method of seismic design of building structures considering earthquake sequences.

7 Transparency statement

This manuscript is a part of the research project (JSPS KAKENHI Grant Number JP23K0416). The part of finding from this research project have been reported in the work previously published (Fujii, 2025a), Seismic response of reinforced concrete moment-resisting frame with steel damper columns under earthquake sequences: evaluation using extended critical pseudo-multi impulse analysis. Frontiers in Built Environment. 11, 1561534]. The same structural model (Dp100 in this manuscript) is used in the previous work, while the other models (Dp033 and Dp050) are the models newly created for this study, as variants of the model Dp100. The previous work was focused on the proposal of the extended ICPMIA and its applicability for the predicting the responses of RC MRFs with SDCs subjected to earthquake sequences. Meanwhile, this work is the parametric study of RC MRFs with SDCs using the extended ICPMIA, focusing on the basic behaviors of RC MRFs with SDCs subjected to sequential seismic input (e.g., the response period of structures, energy dissipation of RC MRFs and SDCs). In this parametric study, influence of the strength balance of RC MRFs and SDCs to the response under sequential seismic input, which cannot be included in the previous study, is also investigated. The analysis data shown in this manuscript is originally created in this study and unpublished previously.

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