Computational Technology Resources - CCP

Keywords: passive control, genetic algorithms, optimization, safety, dynamical analysis.

Summary

Since 1997, it has been obligatory in Italy, to install safety systems that conform to the UNI - EN 795 Standard - "Protection against falls from a height" [1]. The people who work in a hazardous area or work at a height have to work in safety.

An example of useful fall protections is the installation of Safety Line systems. These systems consist in one or more fixed cables to which the workers can be connected with a moving cable. In this way, the safety of the worker is assured if the cables systems are dimensioned to resist the worker weight increased by the dynamic effect, with a proper safety coefficient.

In the Safety Line system, the presence of dissipative devices is very important to reduce the axial force in the cable during the possible fall of a body. This paper analyzes the dynamic response of a Safety Line installed by the Italian Society "Nuovo Modulo S.p.A." [2] on its new buildings. The purpose of these research is to investigate, with numerical simulations for an actual case, the importance of a proper design of the dissipative device.

In order to understand the importance of the dissipative device, the dynamic response was analyzed for two structural systems: the first without dissipative device at the anchorage and the second with an optimized dissipative device. The numerical model was developed using the ADINA finite element program [3] while the optimization process was performed by a genetic algorithm approach [4,5].

Table 1 summarizes the comparison between the response evaluated on the system without a dissipative device (without d.d.) and the response of the system with dissipative device (with d.d.).

Table 1: Comparison between the response without dissipative device (Without d.d.) and the response of the system with dissipative device (With d.d.).
	Without d.d.	With d.d.	Difference (%)
Maximum displacement	0.75 m	0.85 m	+ 13%
Medium displacement	0.50 m	0.80 m	+ 60%
Oscillation amplitude	0.40	0.05 m	- 87%
Maximum axial tension	13000 N	9000 N	- 31%
Medium axial tension	7000 N	4000 N	-43%
Oscillation amplitude	8000 N	1500 N	-81%

From the values reported in Table 1, one notes that the dissipative device provides many improvements to the system:

A decrease of about 90% of the mass oscillation after the fall.
A decrease of about 30% of the maximum axial force on the anchorage.
A decrease of about 80% of the oscillation amplitude of the axial force on the anchorage.

For these reasons, one can conclude that a proper design of the dissipative device plays a fundamental role in order to have a good behaviour of the whole safety system.

References

1: UNI - EN 795 Standard - "Protection against falls from a height".
2: Nouvo Modulo S.p.A., available on-line: www.nuovomodulo.com
3: The home page of the structural codes ADINA - www.adina.com
4: L. Sgambi, F. Bontempi, "A genetic algorithm approach for performance evaluation of long span suspension bridges", in B.H.V. Topping, (Editor), "Proceedings of the Tenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirling, UK, paper 3, 2005. doi:10.4203/ccp.81.3
5: L. Sgambi, (In Italian) "I metodi dell'intelligenza artifi-ciale nell'analisi e nella progettazione di ponti sospesi", Ph.D. Thesis on Civil Engineering, University of Rome "La Sapienza", Advisor Prof. F. Bontempi. Available on-line padis.uniroma1.it/getfile.py?recid=267

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