Acoustic Design of Super-light Structures

Super-lette konstruktioner er nyudviklet og patenteret konstruktionsprincip for betonkonstruktioner. Det kombinerer nogle af de gode egenskaber af normal stærk beton og letklinkerbeton så materialerne kan blive bedre udnyttet og gør det muligt at designe forbedrede betonkonstruktioner og elementerDet super-lette dæklelement i den nærværende forskning er udviklet som en holistisk design, ved at inkluderer alle relevante discipliner. Elementet er baseret på velkendte teknologier og materialer, der har været brugt i årtusinder, det drejer sig om trykbuer og letvægtsbeton (LECA) sammen med en nyudviklet teknologi kaldet perle-kæde aremering, som er et system for efterspænding . Her er det vist hvordan man kan kombinere disse teknologier i et præ-fabrikeret super-let dækelement, mens kravene til et holistisk design er honoreret.Akustiske målinger er blevet udført med elementet i et kontrolleret laboratorie miljø for at evaluere dets præstation i luftlydsisolering og trinlydsisolering. Disse resultater er blevet anvendt til simuleringer af anketransmission af et super-let dækelement for at vurdere dets in-situ præstation. Flanketransmission er blevet undersøgt i både et standard rum, der består af præ- fabrikerede betonelementer og ved en parametrisk undersøgelse for at vurdere præstationen i et ukendt rum og for at vurdere nøjagtigheden af den anvendte model.Forsøg af brudgrænsetilstanden mht. moment-, forskydnings- og forankrings bæreevner er udført for det super-lette element. Som en del af den samme eksperimentelle testserie er de elastiske strukturelle egenskaber af det superlette element også undersøgt. Dette gøres for at kontrollere, at kravene og fremgangsmåderne der er specificerede i design standarderne kan anvendes til dækelementet med tilstrækkelig nøjagtighed. Desuden har det super-lette dækelement succesfuldt været udsat for en to timers lang standard brandprøvning.En modificeret udgave af det superlette element er blevet brugt til et demo-project, hvor indendørs gangbroer er blevet designet og bygget. Understøtnings betingelserne er komplicerede da der er stor mængde punkt understøtninger. Dette krævede en høj grad af tilpasning af det super-lette dækelement, hvor flere kendte teknologier er blevet integreret, samt udviklet til det super-lette dækelement med henblik på at kunne konstruere gangbroerne.Super-light structures is a newly developed and patented construction principle for concrete structures. It combines some of the desirable properties of normal strong concrete and lightweight aggregate concrete in order to improve the utilization of the materials and to design improved concrete structures and elements.The super-light slab element in the present research is developed as a holistic design including all relevant disciplines. The element is based on wellknown technologies and materials, which have been used for millenniums, namely compression arches and lightweight expanded clay aggregate (leca) along with a newly developed technology called pearl-chain reinforcement, which is a system for post-tensioning. Here, it is shown how to combine these technologies within a precast super-light slab element, while honoring the requirements of a holistic design.Acoustic experiments in a controlled laboratory environment have been conducted with the element in order to evaluate its performance in airborne and impact sound insulation. These results have been employed in simulations of the flanking transmission to estimate the in-situ performance of the super-light slab element. The flanking transmission has been done both in a standard room consisting of precast concrete elements and as a parametric study in order to estimate the accuracy of the used model.Experiments on the ultimate limit state regarding moment, shear and pull-out resistance is carried out for the super-light element. As a part of the same test series elastic behaviour of the super-light element is also investigated. This is done to verify that requirements and methods supplied by design codes can be applied to the element with sufficient accuracy. In addition, the super-light slab element has been exposed to a standard fire test.A demo project, where a variation of the super-light element is included as indoor pedestrian bridges, has been designed and constructed. The support system was complicated and included a high amount of point supports. This required a high degree of versatility of the super-light element, as several known technologies were integrated and developed for the super-light element, in order to construct the pedestrian bridges

My first employee: an empirical investigation

The challenge for solo entrepreneurs to add their first employee is arguably the single biggest growth event facing any growing firm. To understand how this event affects performance, and the antecedents of hiring, we analyse Danish matched employer-employee data. Those who hire enjoy superior sales outcomes in subsequent years, while the dispersion in profits increases. Furthermore, those that hire enjoy faster sales growth in the previous year, suggesting that sales growth precedes the first hire. Finally, we show that founders with a stronger profile in terms of education and previous income are more likely to increase profits, while the characteristics of the employee are less important. The latter finding is important from a job creation perspective, in light of the suggested sorting of more marginalized employees into new and established firms

KCl-induced corrosion of Ni-based alloys containing 35–45 wt% Cr

Ni–(35–45)Cr–4Nb alloys containing different fractions of α-Cr were exposed to potassium chloride (KCl)-induced corrosion. The corrosion exposures were carried out for 168 hr at 600\ub0C in a 15% (vol/vol) H2O (g) + 5% (vol/vol) O2 (g) + N2 (g; balance) atmosphere using KCl-free (reference) and predeposited KCl samples. To mimic the KCl deposition in real boilers, 24 hr exposures where KCl vapor condensed continuously onto samples were also performed. The corrosion attack of the studied materials increased significantly when KCl was present compared to the KCl-free samples. For the KCl exposures, the corrosion attack drastically increased when a significant α-Cr fraction was present. α-Cr was either selectively attacked or dissolved through solid-state diffusion and a layered build-up of the outer external scale of K2CrO4 and chromia could be observed. For the in situ condensed KCl exposure, severe corrosion was observed already within the 24 hr exposure, indicating a higher corrosion rate compared with when KCl was predeposited