In this paper, ANSYS/LS-DYNA dynamic analysis software was used to establish finite element truss models with six trusses. The models with impact loads aimed to simulate the scenarios that structures were crashed by heavy truck. By changing the crashed position, the impact load intensity and structure height-span ratio, the models could give out the structural performance, including the stress, strain and other impacts in different scenarios. Besides, considering the component failure, this paper analyzed the possibility of structural progressive collapse. Results for the load cases from below indicate that it will be more destructive if impact load is arranged on 3rd side pillar and progressive collapse will occur if pillar fails after crashed.
Truss structure, which is one of the most widely used architectural structures, is generally used in gymnasiums, museums, theaters and terminals, and other public buildings [1]. Numbers of links in truss structure result in complex distributions of natural vibration, which increase the difficulty of analyzing [2]. With the increasing number of automobiles, the possibility of vehicle impact rises [3]. Xingguo Wang and Youpo Su studied the performance of reinforced concrete frame under impact [4]. Yan Xiao and Lin Chen did some researches on truss protection effect under the vehicle impact [5]. Hui Qu and Jingsi Huo verified the truss performance discipline by experiments on dynamic plastic loading of frames [6]. Hyungoo Kang and Jinkoo Kim analyzed the possibility of progressive collapse of steel moment frames subjected to vehicle impact [7]. Currently, most of the researches about vehicle impact mainly focus on bridges. Researches about the performance of truss under impact are limited but meaningful. This paper analyzed the effect of impact loads on mechanical performance for truss structure by finite element truss models built with ANSYS/LS-DYNA dynamic analysis software.
2. Truss Structure Model
The models were established by ANSYS/LS-DYNA dynamic analysis software. The parameter of model is shown in following Table 1, Table 2 and Figure 1.
3. Loads Position Effects Exploration
Assuming the truck density is 148 kg/m3 (weight is 8 t), then the impact load intensity is 8 × 104 kg∙m/s (8 t × 10 m/s). Considering the symmetry of the structure, Table 3 and Figure 2 show the performance of structure under impact loads on four positons.
The results indicate that loads on the 3rd side pillar will result in maximum stress in the structure, which is most destructive.
4. Bearable Maximum Impact Load Exploration
Through assuming different density of impactors and constant size and velocity, different impact loads could be arranged on truss. Table 4 shows the performance of structure under different intensity of impact loads and Figure 3 shows the
Parameters of basic truss model
Element
Truss Structure
Truck
Unit
Link160
Beam161
Shell163
Solid164
Size
diameter: 0.048 m span: 28 m truss number: 6
Inner diameter: 0.20 m outer diameter: 0.14 m height: 9 m
thickness: 0.03 m
length: 6 m width: 3 m height: 2.5 m velocity: 10 m/s
Parameters of structural material
Density
EX
Failure strain
Yield stress
NUXY
Tangent module
7850 kg/m3
2.06 × 1011
5%
3.45 × 108 Pa
0.3
6.1 × 109
Truss structure model and truck model.
performance of truss under No. 7 load.
Table 4 and Figure 3 indicate that the bearable maximum impact load intensity truss is about 1.8 × 105 kg∙m/s (18 t × 10 m/s). With 2 × 105 kg∙m/s (20 t × 10 m/s) loads, the maximum stress in structure will be yield stress (3.45 × 108 Pa) and the relative deformation in some components will exceed 5%, which could result in structure failure.
5. Height-Span Ratio Effects Exploration
8 × 104 kg∙m/s (8 t × 10 m/s) impact load was arranged on 3rd side pillar in structures with different height-span ratio, and structural performances show in Table 5. The relationship between stress and height/span ratio is displayed in Figure 4.
Structure performance plots under impact load on different positions
Different load positions analysis
No.
Load position
Max-stress
Max-prin strain
Displacement
1
Front-1st
4.14 × 107 Pa
3.38 × 10−4
0.3414 m
2
Side-1st
4.73 × 107 Pa
3.22 × 10−4
0.3302 m
3
Side-2nd
5.15 × 107 Pa
3.05 × 10−4
0.3267 m
4
Side-3rd
6.68 × 107 Pa
2.50 × 10−4
0.3258 m
Impact loads intensity analysis
No.
Load Intensity
Max Stress
Max-prin Strain
Displacement
Notes
1
8 t × 10 m/s
4.14 × 107 Pa
3.38 × 10−4
0.3414 m
2
10 t × 10 m/s
5.73 × 107 Pa
3.92 × 10−4
0.3302 m
3
12 t × 10 m/s
7.14 × 107 Pa
4.45 × 10−4
0.3267 m
4
14 t × 10 m/s
8.67 × 107 Pa
5.51 × 10−4
0.3258 m
5
16 t × 10 m/s
1.043 × 108 Pa
6.77 × 10−4
0.5914 m
6
18 t × 10 m/s
1.246 × 108 Pa
8.08 × 10−4
0.6511 m
7
20 t × 10 m/s
4.349 × 108 Pa
5.94 × 10−4
1.1321 m
Fail
Structure performance plots under No. 7 load
Plot of stress and height/span ratio
Height-span ratio impact analysis
No.
Height-span ratio
Max-stress
Max-prin strain
Displacement
1
0.3214
4.14 × 107 Pa
3.38 × 10−4
0.3414 m
2
0.3571
6.02 × 107 Pa
2.07 × 10−4
0.3623 m
3
0.3929
7.25 × 107 Pa
2.40 × 10−4
0.3645 m
4
0.4286
8.40 × 107 Pa
2.20 × 10−4
0.3551 m
5
0.4643
8.57 × 107 Pa
3.51 × 10−4
0.3498 m
6
0.5000
9.08 × 107 Pa
3.30 × 10−4
0.3492 m
7
0.5357
9.41 × 107 Pa
3.09 × 10−4
0.3497 m
8
0.5714
9.65 × 107 Pa
2.75 × 10−4
0.3501 m
9
0.6071
9.88 × 107 Pa
3.48 × 10−4
0.3578 m
10
0.6429
9.51 × 107 Pa
2.62 × 10−4
0.3521 m
11
0.6786
9.76 × 107 Pa
2.67 × 10−4
0.3499 m
12
0.7143
1.01 × 108 Pa
2.79 × 10−4
0.3541 m
13
0.7500
1.039 × 108 Pa
3.82 × 10−4
0.3614 m
6. The Possibility of Progressive Collapse Analysis
The axial load in the 3rd side pillar was about 20 kN. For analyzing the possibility of progressive collapse, the failure part (3rd pillar) was removed and the inverse axial load was arranged on the same position, which was demonstrated in Figure 5. Besides the slack load, showed in Table 6 was arranged on the truss.
As it was showed in Figure 6, components will progressively fail and truss will collapse finally if the 3rd side pillar fails due to impact.
Inverse axial load on failed pillar position
Results of progressive collapse analysis
Time groups and loads groups
Group
1
2
3
T
0 s
1 s
Q
−20 kN
−20 kN
F
1000 kN
1000 kN
T1
0 s
0.033 s
1 s
FT
−1000 kN
−1000 kN
7. Conclusions
In this paper, the finite element truss model with six trusses was established with ANSYS/LS-DYNA dynamic analysis software. It simulated the situations that structures were crashed by heavy truck. Through changing variables, such as the crash positions, the impact load intensity and structural height-span ratio, this paper concluded their effects to the stress and strain in truss structure. Besides, considering the component failure, this paper analyzed the possibility of structural progressive collapse. Conclusions are shown as below:
1) Impact load on the 3rd side pillar will result in maximum stress in the structure, which is most destructive. The bearable maximum impact load intensity truss is about 1.8 × 105 kg∙m/s (18 t × 10 m/s).
2) The stress will be stronger in truss with greater height-span ratio. When the ratio is less than 0.6, the maximum stress in structure will increase by 1 × 107 Pa with ratio increasing by 0.05. When the ratio is more than 0.6, is has not significant effect to the stress.
3) If the 3rd side pillar fails due to impact, components will progressively fail and the truss structure will collapse even though the impact load intensity is less than 1.8 × 105 kg∙m/s (18 t × 10 m/s).
Cite this paper
Zheng, Z.W. and Bai, Y. (2017) Effects of Impact Loads on Mechanical Performance for Truss Structure. World Journal of Engineering and Technology, 5, 135-140. https://doi.org/10.4236/wjet.2017.53B015
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https://doi.org/10.1016/j.tws.2016.11.023Kang, H. and Kim, J. (2015) Progressive Collapse of Steel Moment Frames Subjected to Vehicle Impact. Journal of Performance of Constructed Facilities, 29, 04014172. https://doi.org/10.1061/(ASCE)CF.1943-5509.0000665