# Measurement and Analysis of Vibration Levels for Truck Transport Environment in Korea
## 1 Introduction
[11] developed two PDS profiles based on 70% of vehicle vibration signals with the lowest acceleration levels and 30% with the highest. However, this method is too subjective for dividing the upper and lower ratios in the PSD calculation. For example, [PERSON] [12] used an 80:20 percentage ratio, and [PERSON] [7] used three-way split spectra of 70:25:5 for the signal. Even if the PSD is calculated by taking only the upper group of high-amplitude events, the distribution is still Gaussian, but the high-amplitude events included in the transport  
Figure 1: Concept of random vibration. vibration signal are integrated at random points within the signal. Thus, this approach allows for better simulation of the overall distribution of vibration acceleration [13]. In several geographic regions including North America [11; 14; 15; 16], Australia [17], Japan [9; 17], China [18], India [19], Brazil [20], Spain [21], Thailand [22] and Hungary [23; 24; 25], vibration, and shock measured in representative vehicles in each country's vehicle transport environment have been published. Also, many researchers have compared their measurement results with existing global standardized test protocols such as ASTM [26], ISO [27], and ISTA [28]. The causes of vehicle transport vibration can be divided into three main categories: (1) the road roughness, (2) road surface aberrations such as cracks, speed bumps, and potholes, and (3) the vehicle drivetrain system including the wheels, drivetrain, and engine. Because the vibration level in vehicle transport depends on the interaction of the track-truck system, the vibration level is at least a function of road surface classification, terrain configuration, vehicle speed, vehicle suspension type and its conditions, load configuration, and tire pressure [7; 8; 9; 11; 14; 18; 21; 22]. Lead by [PERSON] and [PERSON] [15], several researchers [11; 13; 19] have divided the vibration frequency of trucks into three significant ranges: (1) 3-4 Hz, representing the truck suspension response; (2) 15-20 Hz, representing the tire response; and (3) 40-55 Hz, representing the structure response. According to the results in the published literature, the vibration levels in air-ride trucks are significantly lower than those in leaf-spring trucks [11; 15; 16; 18; 21; 29]. [PERSON] et al. [16] stated that the vibration levels of leaf-spring trailers are at least 50% higher than those of air-ride trailers. However, [PERSON] and [PERSON] [15] reported that a truck with damaged air-ride suspension result in significantly higher vibration levels than those with leaf-spring suspensions. They reported predominant suspension frequencies of air-ride and leaf-spring trailers of 2 Hz and 3-4 Hz, respectively; [PERSON] et al. [21] reported similar results. [PERSON] and [PERSON] [30] reported that vibration peaks in leaf-spring and the air-ride suspension trucks occur at frequencies of 3 Hz and 4 Hz, respectively. The vibration level is shown to increase with an increase in vehicle travel speed, with a smaller the payload resulting in higher vibration levels [8; 15; 18; 21; 31]. However, singh and [PERSON] [15] stated that the vibration levels increase significantly in air-ride trailers because the air-ride suspension becomes stiffer as the trailer load increases. The vertical vibration level was shown to be larger than the lateral and longitudinal vibration levels [11; 14; 31], and the vibration levels according to the location of the truck platform is more significant at the rear than at the front [15; 29]. To apply PSD profiles obtained under various conditions to the simulation, a composite PSD profile with simplified breakpoints representing these conditions be determined. Generally, a smoothing process is valid for simplification of a single PSD profile [12; 23]. However, two methods have been used to create a composite PSD profile representing several PSD profiles obtained under various conditions.