The presentation describe the rockfall trajectories analysis realized with Rockyfor3D software from Ecorisq
Thomas
24/03/15
01/11/14
Probability vs fate
Is more probability calculus or fate....???
Thomas
07/01/13
Deviation lower lateral cable on rockfall barrier
In many cases the rockfall protection barriers must adapt to the conditions of the terrein. One of the points that require greater attention and detail to guarantee the structural strength of the rock barriers is te deviation on lower lateral cable. In the drawing belowe you can see two typical case but not the only one. You may need to resolve deviations elevation (as in drawings) and planimetric.
Case n°1: lateral lower cable deviation
Case n°2: intermediate lower cable deviation
In many cases it is the experience of the engineer on site or installation company that allow you to solve the problem...but....
....after the Guideline ETAG027/2008, the variation of geometry of the rockfall barriers respect to the tested barrier will be guaranteed by the manufacturer with special calculation as as described in chapter 4.3:
"If for local reasons of the natural site it is necessary to have a different geometry from the test site geometry a specific design shall be provided. Forces acting in the structure should be evaluated to demonstrate the fitness for use of the falling rock protection kit. The producer, under its own responsibility, shall provide geometric tolerances in the installation book with special references to the spacing of the posts and the inclination of the main ropes".
I don't understand if the responsibility to define what forces act on the modified structure are in charge of the manufacturer or designer???
And today for my experiences I've never found a manual with described tolerances permitted for the deviation of lower/lateral cable.
Who can clarify this issue?
Thomas
04/12/11
Two or one alignment of rockfall barriers?? - Part 1
Recently news on high energies rockfall protection barrier has opened a discussion on the energy lmitis of the rockfall protection steel barrier.
Many people have asked me this: is a 8000kJ barrier equal to two allignment of 4000kJ barriers when impacted from the same block?? (see the image belowe).
The answer is very difficult and dipending to differnet factors.
To try answer I make before some considerations (we refer for example to ETAG027 guideline procedure testing):
- for the 4000kJ barrier (tested follow ETAG027) we don't know the behavior when impacted with an energy (ex. 8000kJ) greater than test energy (just 4000kJ);
- for the 4000kJ barrier (tested follow ETAG027) we don't know the behavior when impacted with a mass and velocity different from the test
For this reasons, if the impact energy is greater than the MEL Energy of the barrier, we can't say that (see drawing belowe):
...if we make this error we don't take in account the structrural behavior of rockfall steel barrier.
For this reason my firs answer is that 4000kJ+4000kJ is different than 8000kJ in terms of behavior of structure..... but I don't know if 4000kJ+4000kJ is greater or lesser than 8000kJ.
In a next post I try to find a model to calculate the energy exit of the rockfall barriers (E-out) and try to answer to the question.
Discussion open !!!
Thomas
23/08/11
Rolling Stones in New Zeland and Height Design of Protective Measures
For many people it is difficult to understand the motion concept of rocks along the slopes, in this interesting video shot in New Zealand (Christchurch) from GNScience Chris Massey analyses rockfall hazards to assist Christchurch recovery planning and discusses many issues related to unpredictable prevents this phenomenon.
At 4.17 minute of the video is very interesting to observe the deviation of the block (aprx. 40 °) respect the line of maximum slope angle ........ only for a little impact point with a rock outcrop present on the slope.!!!!!
This is very difficult to take into account with the rockfall analisys two dimensional and probably for this type of activities the better solutions is the 3D software.
In any case for my experiences the rebounding height is much more unpredictable than the rock energy. For this reason, my assumption design of heght protection measures is based on model described belowe.
Probably can be other parameter to take in accont and in this way are welcome advice on other experiences.
ciaoooo
Thomas
27/04/11
Bushfire on steel mesh - Effetti degli incendi sulle reti in aderenza
Some time ago I discussed with professor A.G. Meyers form Rocktest Australia the problem of bushfire on steel mesh.
Prof. Meyers live in Australia where during bushfire the temperatures at ground level can exceed 800oC.
I asked professor Meyers to write something on this topic to be published on the rockfall BLOG......these are his words:
"In areas prone to bushfires, it is possible that at least part of a draped mesh installation may be subjected to a bushfire (see down photos). In such cases, it is prudent to consider how a fire may affect the integrity and longevity of the mesh.
In Australian bushfires, temperatures at ground level can exceed 800oC for periods of up to 120 seconds. The temperatures then tend to decrease rapidly as a flame front passes. Consider how such an event may affect the PVC coated, galvanised wires from which some meshes are woven.
As a bushfire approaches a mesh, the PVC will begin to soften at 75oC and then melt. The PVC will no longer provide any subsequent corrosion protection to the wire.
Zinc is used in a standard galvanising process to provide cathodic protection to the steel. Zinc melts at 420°, significantly less than the temperature of a bushfire. However, free zinc tends to occur only near the surface of the coating. There may not therefore be a significant loss in the total mass of the coating if this free zinc melts.
Most of the coating comprises a zinciron alloy that forms when the zinc reacts with the iron in the wire. The heat of the zinc during the hot-dipping process causes the surface of the steel to become porous at the molecular scale allowing alloying to occur within the pores. The alloy has a melting point of approximately 650oC; a temperature less than that possible in a bushfire. However, as found by Bennets & Thomas (1994), the temperature of 3mm thick steel tends not to exceed 430oC when subjected to a temperature similar to that applicable to a bushfire for a similar time. There may not therefore be a significant loss in the total mass of the coating due to melting of the alloy as the bushfire passes.
Another possible occurrence is that the alloy coating may crack as the volume of the steel increases more than that of the coating due to differences in the thermal expansion coefficients of the two materials. However, cracking may not be too great a concern as the coefficient for the alloy tends to be higher than that for the steel.
Another possible occurrence relates to smoke deposits and humidity in the air that can produce an acidic solution after the bushfire has passed. There can be an increase in the rate at which the coating corrodes if the solution settles and remains on the alloy. However, in most cases, the solution gets diluted rapidly by subsequent rainfall and no longer is a significant problem.
To confirm the above conclusions, samples of wire (see photos down) were obtained from a draped mesh that had been subjected to one of many bushfires that occur in the hills above Adelaide, South Australia. Samples were obtained immediately after the fire and one year after it had occurred. Samples were also obtained from a mesh from the same batch that had not been subjected to a bushfire. The thicknesses of all wires were measured. There was no significant measurable loss of thickness in any wire. The burnt wires were also viewed under a microscope which indicated that there had been no obvious evidence of crack development.
Figure 2. Close up of double twist, PVC coated, galvanised, wire sampled from burnt mesh.
The conclusion was reached that a mesh, woven from PVC coated galvanised wire subjected to a bushfire, is likely to corrode at a rate similar to that for a galvanised mesh without a PVC coating. It is however difficult to ascertain what this rate may be as it tends to vary according to location, environment, thickness and quality of galvanising, characteristics of the steel and mesh installation conditions and details.
Reference: Bennetts, I.D. & Thomas, I.R. 1994. Developments in the design of buildings for fire safety. Preprints of papers in Australasian Structural Engineering Conference (ASEC94), IEAust., Vol 2. Sept. 1994: 640-645."
Tank you to Peter for this interesting text that allows us to increase our knowledge in this field.
Thomas
09/07/10
30/04/10
ETAG027 e tipologie di campo prova
Una delle domande che i + mi sottopongono è se la nuova Linea Guida Etag027 vincola il produttore all'utilizzo di una determinata tipologia di campo prove (verticale, inclinato, orriziontale...)??
...la risposta è NO!!!! e vediamo il perchè...
.....nella stesura della linea guida c'è stata una dura battaglia fra componenti della commissione EOTA (rif. ETAG027) per evitare che potessero emergere delle posizioni dominanti di tipologie di campo prove di un tipo piuttosto che dell'altro e che in generale avessere potuto avantaggiare un produttore piuttosto che altro...infatti in quel periodo le tre tipologie di campo prove che andavano per la maggiore erano:
1. obliquo a teleferica (italia, francia, austria...forse altri...non so!!)
2. caduta vertcale (svizzera, italia...)
3. orizzontale (giappone...).....qui trovate un video
Con la linea guida Etag027 si è voluto lasciare spazio ad ognuna di queste specifiche tipologie inserendo così come si evince al punto 1.4.2.13 (Fig.3) che riporto qui di seguito.
Spero possa essere stato chiarificatorio per tutti...
ciao Thomas