# Performance and Measurement Devices for Membrane Buildings in Civil Engineering: A Review
## 3 Performance
### Air-Supported Membrane Structure
#### 3.1.4 Impact Load  
It is challenging to disregard the impact effects created by external collisions that induce high vibrations in membrane structures. In nature, the impact load on the structure has unknown properties, resulting in stochastic vibration and deformation [74]. Large deformations may reduce the structural pretension, rendering the structure unserviceable afterward when subjected to wind loads below the design value [75]. Similarly, a low tear strength in the membrane leaves the structure susceptible to scratches and punctures by impact objects [76]. Therefore, impact load is an essential factor that has to be considered in the design of membrane structures, but it is not included in the calculation of the load-effect combination in existing design codes and standards of membrane structures [77]. The experiment of the planar membrane with the self-made ballistic launcher or drop-weight machine is the basic approach to studying the influence of impact load on a structure. [PERSON] et al. [78] examined the effect of pretension on vibration induced by impact load. When pretension increased, the amplitude of the vibration frequency increase was nonlinear and showed a downward trend. Moreover, [PERSON] et al. [79] found that pretension plays a dominant role in stochastic vibration relative to other parameters. Strong random vibration had pronounced nonlinearity. The probability density function (PDF) results of the dynamic response were close to Rayleigh distribution. Weak random vibration had a tendency to be linear, while the PDF results appeared to follow a Gaussian distribution [79; 80]. For the circular tensile membrane, the smaller the radius, the larger the maximum amplitude, velocity, and acceleration and the smaller the natural frequency, reflecting the more significant dynamic response [81]. [PERSON] et al. [82] reported that, in the early stages of the vibration, high-frequency vibrations were induced due to the interaction between the incident waves from the impact and the reflected waves from the side cables, as illustrated by the M-shape in the peak displacement region of the displacement time curve in Figure 13. Furthermore, the maximum incident displacement increased with the increase in pretension. Figure 12: Structural deformation under different wind speeds (side view) [19]. Figure 13: Time course curve of tensioned membrane displacement affected by impact loading [82]. As an extreme natural phenomenon, hail is a typical impact load on structures. [PERSON] et al. [75; 77; 83] designed an experimental device to study the effects of hail on saddle-shaped and umbrella-shaped tensile membranes. Silicone balls of different sizes were utilized to mimic hail and randomly impacted the membrane surface through a sieve, as shown in Figure 14. Under normal conditions, hail did not cause structural failure. However, a considerable displacement of the membrane surface was caused by the impact of hail, which might render plastic strain on the membrane and cause a severe decline in structural pretension. For the saddle-shaped tensioned membrane, the loss of pretension was mitigated by the increasing rise-span ratio [75]. Rainfall generally has no noticeable effect on membrane structure, but the dynamic response caused by heavy rainfall has attracted attention in recent years. Artificial rainfall devices are able to successfully simulate rainfall parameters consistent with natural rainfall and successfully regulate parameter variation, which is one of the approaches to examining the impact of heavy rainfall on structures [84]. An artificial rainfall device is shown in Figure 15. [PERSON] et al. [85] reported that the diameter of raindrops and their impact loads on a structure followed the Weibull distribution and generalized extreme value distribution, respectively. The displacement response of the structure obeyed non-Gaussian distribution with tail characteristics. Stronger nonlinear vibrations were excited by water accumulation in a horizontal membrane structure according to [PERSON] et al.