###### Abstract
Among the GMD definitions reported in the literature, the bracketed duration (BD, \(T_{B}\)), the uniform duration (UD, \(T_{U}\)), the significant duration (SD, \(T_{S}\)), and the effective duration (ED, \(T_{E}\)) have been demonstrated to be the most appropriate indicators of the inelastic dynamic analysis of structures [19]. Recently, [PERSON] et al. [4] suggested that the integrated duration of the multi-directional duration characteristics may be assessed using the SD index; they also analyzed the effects of diverse direction duration on dam failure modes. [PERSON] et al. [3] studied the impact of the GMs with a longer and a shorter SD on the total cumulative energy wasted in seismic isolation systems. [PERSON] et al. [17] evaluated the effect of the GMD on the structural deterioration observed in a variety of frame structures. [PERSON] et al. [20] discovered that a longer SD significantly increases the failure probabilities of the earth slopes. [PERSON] et al. [21] employed the SD index to express the cumulative damage characteristics of deeply-burried hydraulic tunnels. It is important to note that most of the research cited above employs the acceleration-type duration index to determine the influence of the seismic duration on the structural reaction, while ignoring the velocity pulse effect. As such, the acceleration-type GMD indicators may not be suitable for illustrating the impact of the pulse-type NFGM duration on the structural response [22]. Therefore, it is necessary to employ an efficient velocity-type GMD index that can consider the essential characteristics of the significant velocity pulse duration of the NFGMs. During the dynamic analysis of underground structures, the dynamic time-domain response analysis methodology is frequently used in the finite element (FE) numerical computation of underground structures [23; 24; 25; 26; 27; 28; 29; 30], since this methodology has the adaptability to capture complex structural responses. The methodology generally starts with selecting the as-recorded GMs appropriately and treating them as seismic excitations acting on the complex structural system. Subsequently, the FE model with a multi-degree system is addressed using a step-by-step integration method at each moment in the time domain [31]. In this analysis process, the time consumed by the underground structures far exceeds the total duration of the as-recorded GMs, as do the many human and material resources consumed. However, the effective duration of the pulse-type NFGMs may be mainly concentrated in the time-history curve of the large velocity pulse of the low-frequencycomponents, which has a much shorter duration than the total duration of the NFGMs. The question of how to propose a simple, reliable, and convenient methodology to reduce the total time of the as-recorded NFGMs, is a frontier challenge essential for civil designers, in order to enhance the calculation efficiency and reduce computational costs. Based on the above considerations, the purpose of this paper is to gain an understanding of the influence of the duration of the pulse-type NFGMs on the seismic performance of hydraulic tunnels built deep underground. A velocity-type duration index is presented in Section 2. Subsequently, the selection criteria for the NFGMs with the velocity pulse and the corresponding duration are briefly illustrated in Section 3. In Section 4, the geometry of the hydraulic tunnel and the FE numerical model are illustrated. The effect of the velocity-type NFGM duration on the inelastic dynamic response and the damage pattern are discussed in Section 5. The applicability of a strong duration index and reduced time-history methodology are evaluated in Section 6. The summaries and conclusions follow in Section 7.