Experimental investigation on the dynamic response of RC flat slabs after a sudden column loss

To prevent disproportionate collapse under an extreme loading event, a sudden column loss scenario is often used to ensure the structure has suitable robustness. This study aims to investigate experimentally the dynamic response of reinforced concrete flat slabs after a sudden column loss. Seven 1/3 scale reinforced concrete flat slabs were tested under static load increases or dynamic column removal cases with different supports removed. Reaction forces and deflections were recorded throughout, along with reinforcement strains and concrete cracking patterns. During dynamic tests, a high speed camera was used to capture the dynamic motion. The experiments demonstrated that flat slabs, in general, are able to redistribute their loading effectively after a column loss. Although large levels of damage were observed, collapse due to flexural failure did not occur. However, punching shear was shown to be an issue due to the additional vertical loading on the adjacent supports. The inclusion of continuous bottom reinforcement through a column did not significantly improve the capacity, as the new load path is not primarily through the removed column location. The results also indicate that the dynamic effects due to a sudden column loss can be significant as deflections of up to 1.5 times the static case were measured within the elastic range. It is also shown that the Dynamic Amplification Factor (DAF) reduces when nonlinear damaging effects are included, which implies conventional code-based design methods for flat slab structures may be over conservative. Additionally, the increase in material strength due the strain rates is not viewed to be significant

Dynamic column loss analysis of reinforced concrete flat slabs

The sudden column loss idealisation is a useful design tool to assess structures for progressive collapse. As such an event is a dynamic problem, suitable account must be taken of these effects. This can either be achieved by a full dynamic analysis of the structure or a simplified static approach, with correction factors for the dynamic influence. This study aims to investigate the response of Reinforced Concrete (RC) flat slab structures after a column loss using experimentally validated Finite Element (FE) models. The nonlinear dynamic response of a structure after such an event is considered, including the redistribution of loads and displacement profile. These results are then compared to equivalent static cases in order to determine the Dynamic Amplification Factor (DAF). For the range of structures considered, the DAF was calculated as between 1.39 and 1.62 for displacements, with lower factors associated with a higher nonlinear response or slower column removal. Additionally, the shear forces in remaining columns may exceed 200% of their fully supported condition, with a different associated DAF. The effects of increasing the tensile strength of concrete due to high strain rates are also considered. Typical Dynamic Increase Factors (DIFs) based on the strain rates were up to 1.23, however, this only applied for a short time period, and in a limited area. Therefore, such effects do not significantly influence the response

Unique fine scale village spatial-temporal distributions of Anopheles farauti differ by physiological state and sex

Background: The ecology of many mosquitoes, including Anopheles farauti, the dominant malaria vector in the southwest Pacific including the Solomon Islands, remains inadequately understood. Studies to map fine scale vector distributions are biased when trapping techniques use lures that will influence the natural movements of mosquitoes by attracting them to traps. However, passive collection methods allow the detailed natural distributions of vector populations by sex and physiological states to be revealed. Methods: The barrier screen, a passive mosquito collection method along with human landing catches were used to record An. farauti distributions over time and space in two Solomon Island villages from May 2016 to July 2017. Results: Temporal and spatial distributions of over 15,000 mosquitoes, including males as well as unfed, host seeking, blood-fed, non-blood fed and gravid females were mapped. These spatial and temporal patterns varied by species, sex and physiological state. Sugar-fed An. farauti were mostly collected between 10–20 m away from houses with peak activity from 18:00 to 19:00 h. Male An. farauti were mostly collected greater than 20 m from houses with peak activity from 19:00 to 20:00 h. Conclusions: Anopheles farauti subpopulations, as defined by physiological state and sex, are heterogeneously distributed in Solomon Island villages. Understanding the basis for these observed heterogeneities will lead to more accurate surveillance of mosquitoes and will enable spatial targeting of interventions for greater efficiency and effectiveness of vector control

Thermal conditions in stereolithography injection mould tooling

The use of stereolithography (SL) as a rapid tooling technique for injection moulding provides a low cost and quick alternative to hard tooling methods when producing a small quantity of parts. However, previous work has shown that different characteristics are developed by crystalline plastic parts produced from SL moulds and those produced from conventional tooling methods. Differing characteristics means that the parts are not truly the same as those that would be produced by hard tooling and highlights a disadvantage to SL tooling. Such differences are due to the cooling rate experienced by the part. Parts produced from SL moulds are cooled more slowly than those from metal tools as a result of the differing thermal conductivity of the mould material itself. This work concerned establishing the extent of the difference in the heat transfer characteristics. The different cooling rates were demonstrated by real-time data acquisition. The results illustrated the very different thermal history imparted on the moulding that are likely to be the cause of characteristical differences in the parts. The work then describes how the thermal conditions experienced in stereolithography moulds can be used to an advantage. A case study details the use of SL moulds for the injection moulding of polyether-ether-ketone (PEEK) which has high process parameter demands. The results of the case study have shown that not only is the stereolithography rapid tooling method capable of producing a low volume of PEEK parts, but also under conditions that would not be possible using a metal mould. The thermal characteristics of stereolithography moulds allowed fully crystalline PEEK parts to be produced with the mould at room temperature; the equivalent steel mould would require a pre-moulding temperature of ~200 C and much higher injection pressures & speeds