by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
Concrete In Australia : September 2013
58 Concrete in Australia Vol 39 No 3 CONFERENCE EXTENDED ABSTRACT 5.0 RATCHET MECHANISMS IN MODERN CONCRETE STRUCTURES e effect of ratchet mechanisms is rarely addressed in a design context in modern structures, but these effects may arise in any situation where non-recoverable strains occur in a structure or its support. Examples that frequently occur in practice include cracking of concrete, compaction of soils and slip at any friction interface. ese effects can give rise to significant total strains over time and should be considered in structures that may be susceptible, both at design time and as a possible cause when greater than expected movements are observed. Examples of ratchet mechanisms occurring in actual structures are integral bridge abutments, slabs on ground, buried structures, and differential temperature and load cycle effects in flexural members 6.0 CONCLUSIONS Detailed monitoring and analysis of the dome of the Santa Maria del Fiore has built up a convincing picture of the history of crack growth over nearly 600 years, driven primarily by thermal strain effects combined with ratchet mechanisms in the supporting structures. Similar ratchet mechanisms are seen in a wide variety of modern concrete structures, but in most cases these mechanisms are not explicitly recognised in the design process, and analysis and design procedures for dealing with the effects are not well documented. Further research is therefore desirable, both into the effect of ratchet mechanisms on existing structures, and methods of analysing, designing and detailing susceptible structures to minimise any adverse effects. Figure 2. Schematic plan of four major cracks. Figure 1. Estimated development of crack widths from completion to present. 0 0 1 2 3 4 5 6 7 100 Crack width (cm) Time (years) 200 300 400 500 600 1434 -- dome completed 1515 -- "gabbia" completed 1579 -- frescoes completed 1695 -- Nellie's report 1757 -- Ximenes' survey 1895 -- earthquake 1955 -- OPA's system installation