Civil Engineer in South Africa - Volume 34, Issue 11, 1992
Volume 34, Issue 11, 1992
Author J.M. JordaanSource: Civil Engineer in South Africa 34, pp 367 –370 (1992)More Less
At an international symposium held October 1991 in Emeishan City, Sichuan, China, the subjects of debris flow and flood disaster protection were addressed and the present state of the art in debris flow protection and flood control works along some of the railways in China was inspected during guided field trips by train and boat.This technical note highlights some of the many interesting aspects dealt with at the symposium.
Source: Civil Engineer in South Africa 34, pp 371 –378 (1992)More Less
A brief summary is given of the effect of increased strain rates on the resistance value of concrete and reinforcing steel bars. The results of two recent research projects are subsequently reviewed against this background.
The increase in the structural resistance of RC elements is often more than twice the increase in resistance obtained from tests on laboratory coupons of individual constituent materials under corresponding strain rates. Some test results indicate that the increased structural resistance is somewhat greater than the commonly accepted maximum increase of 30 per cent of the static resistance. It appears that this increase may depend on whether the increased strain rate was caused by a hard or soft impact.
Cantilever columns damaged by laterial impact but that recovered substantially from excessive impact deflection displayed full resistance to subsequently applied laterial static load. An important feature typical of RC columns is an increase in axial force resulting from a tendency to lengthen due to transverse cracking that is resisted by the inertia and stiffness of the superstructure.
'n Kort opsomming van die effek wat verhoogde vervormingstempos op die weerstandsvermoe van beton en staalwapening het, word verstrek. Teen hierdie agtergrond word sommige van die resultate soos van twee onlangse navorsingsprojekte verkry, in oenskou geneem.
Die toename in die weerstand van gewapende betonelemente is dikwels dubbel die toename in strukturele weerstand soos van laboratoriumtoetse op monsters van die afsonderlike materiale onder soortgelyke vervormingstempos verkry. Sommige toetsresultate dui op 'n toename in weerstand wat groter is as die algemeen aanvaarde maksimumwaarde van 30 persent. Dit blyk dat hierdie toename daarvan afhang of die verhoogde vervormingstempo veroorsaak is deur 'n harde of sagte botsing.
Kantelkolomme wat deur sydelingse botslaste beskadig was, maar nogtans redelik herstel het van oormatige dinamiese verplasing, was daarna nog in staat om die volle sydelingse statiese las to weerstaan.
'n Belangrike verskynsel wat kenmerkend is van gewapende betonkolomme is die toename in aksiale las wat ontstaan as die kolom in buiging begin kraak en die gevolglike aksiale verlenging teengegaan word deur die traagheid en die styfheid van die bostruktuur.
Author D J StephensSource: Civil Engineer in South Africa 34, pp 379 –380 (1992)More Less
It had previously been shown that the existing prediction models tor the California bearing ratio (CBR) using the soil classification parameters such as grading and the Atterberg limits were unsatisfactory. This note details an investigation that examined the variation of CBR with plasticity index and percentage clay in a series of synthetic soil samples and then proposes a CBR prediction model that allows for the dilution effect of the non-plastic particles in the Atterberg limit tests by using an equivalent liquid limit based on the ratio of these particles and the clay particles. The resulting prediction equation is shown to give satisfactory results for some dolerite, granite and sandstone soil samples.