Seismic Performance of Underground Reservoir Structures

The majority of stiff-unyielding underground structures have performed well in recent earthquakes. The few cases of failure are mainly related to construction in poor ground conditions (e.g., soft fill, liquefiable soils, sloping ground) and inadequate or no seismic design. Currently there is disagreement among engineering professionals and design methodologies on seismic forces and deformations experienced by these structures, sometimes resulting in inaccurate design that maybe un-conservative or over-conservative. The current procedures used to evaluate seismic loading and deformations of these structures rely on over-simplified analytical methods or advance numerical tools that have not been validated against physical model tests. Previous analytical and numerical studies have identified key factors such as structural flexibility, base fixity, and wavelength as being important in the seismic response of these structures. However the commonly used simplified methods don’t take into account these important factors. Further, there is a lack of well-documented case studies and experimental research systematically evaluating the seismic response of stiff-unyielding buried structures that are restrained against excessive deformations at their base and roof. Therefore, a centrifuge experimental study of the seismic response of these structures was performed by varying the key parameters and monitoring seismic lateral earth pressures, racking displacements, bending moments, and soil-structure interaction. The results of these experiments provide a better understanding of the underlying mechanisms of soil-structure interaction near these structures and their overall performance. The results also serve as a database for other researchers to calibrate their numerical tools. A series of sixteen centrifuge model experiments representing 11 to 12 m-high reinforced concrete underground reservoir structures were conducted. The structure stiffness, backfill soil type and slope, embedment, container type (rigid versus flexible boundaries), fixity conditions, and ground motion characteristics were varied to evaluate their influence and relative importance on structural performance. The structures were buried in dry medium-dense sand at 60% relative density and compacted, site-specific silty sand with different backfill slopes. A suit of earthquake ground motions and sinusoidal motions with different frequencies were applied to the buried models. The application of sinusoidal motions in particular allowed for a comprehensive study of the influence of loading frequency in relation to the fundamental frequency of the site and structure

Experimental Studies of Dynamic Response of Foundations

An investigation was made into the behavior of rigid foundations and structures resting on the surface or embedded in a cohesionless soil and subjected to transient active or passive excitations and forced vibrations using the centrifuge modeling technique. The investigation was aimed at studying both low and high amplitude vibrations of foundations under machine type loadings, earthquake or wave induced vibrations, and other sources of dynamic loads. Rigid "prototype" foundations of mass and size comparable to foundations of a low rise building were simulated in the centrifuge at a centrifugal acceleration of 50g. Rigid model structures (aluminum towers) attached to foundations of different shapes, sizes, masses, and moments of inertia were tested. The effect of soil depth, boundary conditions, and depth of foundation embedment were investigated. Mainly rocking and horizontal modes of vibration were studied. The impulse rocking-horizontal excitation of the models was provided by actively perturbing the model structures using explosive energy or by passively exciting them by shaking the whole soil bucket using a hydraulic shaking system. The forced vibration was produced by a miniature air-driven counterrotating eccentric mass shaker mounted on the model structures. During the tests detailed measurements of the static and dynamic contact pressure distributions, displacement components of the model, and acceleration amplitudes at different elevations of the model structure were obtained. The acceleration ratios were used to determine the modes of vibration of the foundation systems. Natural frequencies and damping coefficients of the modes were calculated by fitting the amplitude-frequency response of a single degree of freedom mass-spring-dashpot oscillator to the experimental response curves derived from the test data. Experimental results provided information regarding the influence of different geometrical, inertial, and loading conditions on the vibrational characteristics of the soil-structure system. In particular the effect of foundation embedment was to increase the model resonant frequencies and to cause an appreciable change in contact pressure distribution underneath the footing. However, the resonant frequencies predicted by the lumped parameter analysis for a simple two-degree-of-freedom (rocking and translation) model were about 20 to 55 per cent higher than those measured experimentally. These results were consistent with the comparisons made in similar theoretical and experimental studies such as those performed by Morris in the Cambridge centrifuge and those performed on full-scale footings by Stokoe and Richart. Damping ratios of the rocking-sliding vibration did not change considerably when footing size or depth of embedment changed. The existence of rigid boundaries around the soil mass in the bucket, and an inefficient contact between soil and the foundation side walls and lower surface could account for these observations. Uplift and nonlinear large amplitude vibrations were consistently observed during the steady-state vibration tests. Uplift led to a softer vibrating system which behaved non-linearly. As a result the frequency of vibration decreased with the amount of lift-off. In transient vibration uplift reduced the intensity of higher frequency vibration. Soil around the foundation edge yielded and plastic deformations and subsequent softening of the contact soil increased the material damping while it decreased the resonant frequency of the system. It was concluded that elastic half-space theory does not satisfy the needs for analysis of foundation behavior under high amplitude vibrations and more sophisticated methods of analysis are required.</p

Klimatberäkningar av innerväggar : Comparative climate calculations of 14 different interior walls

För att kunna förändra den klimatpåverkan som genereras av bygg- och anläggningssektorn behöver vi veta var vi står idag. För att sedan kunna ta steget att minska klimatpåverkan från byggnadsmaterial och byggdelar behöver förändringar ske. I januari 2022 införs en ny lag som innebär att alla byggherrar ska ta fram en klimatdeklaration för nya byggnader. Det långsiktiga nationella målet är att Sverige som nation skall ha netto nollutsläpp år 2045. Det lokala initiativet Lokal färdplan Malmö, LFM30, har som mål att Malmös bygg- och anläggningssektor ska vara klimatneutrala redan år 2030. Det finns flera sätt på vilka man kan minska klimatavtrycket från byggsektorn. Ett sätt är att byta ut material som genererar stora utsläpp till material med mindre klimatpåverkan. Ett annat sätt är att göra en LCA på material som ska användas för att utreda dess lämplighet. Studiens syfte är att utreda och föreslå kostnadseffektiva klimatförslag av olika innerväggar. Det kommer göras genom att undersöka om klimatberäkningar av hela byggnader och byggdelar görs idag. Vidare att genom beräkningar visa skillnaderna i klimatpåverkan av olika systeminnerväggar beroende på uppbyggnad och ingående material. Detta för att kunna jämföra väggarna med avseende på koldioxidekvivalenter, CO2e och pris. Tanken är att visa konkreta skillnader i klimatbelastning av innerväggarna och vilka slutsatser som kan dras av en sådan kalkyl. Studien som är utförd med en intervjustudie, beräkningar och genom en fallstudie på ett ROT- projekt har fokuserat på klimatberäkningar av systeminnerväggar. En litteraturstudie har kompletterat övriga metoder för att få en överblick i ämnet. En jämförelsekalkyl av 14 innerväggar med olika material och uppbyggnad är gjord med beräkningar i två program, Bidcon och BM. Resultaten från intervjustudien belyser svårigheterna som finns gällande klimatberäkningar under projektering av en byggnad. Klimatberäkningar under ett projekt är tids- och resurskrävande. Beräkningarna visar att per kvadratmeter innervägg kan man uppnå mer än en halvering av CO2e om man jämför mellan två regelväggar. Väggarna har samma bredd på regel och minskningen beror på material i innerväggen. Skillnaden mellan en innervägg i solid betong och regelväggen med lägst klimatpåverkan är ännu större. Vidare visar beräkningarna att det även går att minska klimatpåverkan från en innervägg med bibehållen kostnad. Studien konstaterar att biobaserade isoleringsmaterial har lägre klimatpåverkan än vad traditionell isolering i form av mineralull har. Träreglar genererar lägre mängd CO2e än vad stålreglar gör. Gällande skivor är skillnaden varken entydig eller stor mellan träbaserade skivor och gipsskivor. Det beror på att resultatet av beräkningarna skiljer sig åt beroende på vilket program som används. Slutsatser av studien är att mycket kan göras för att minska klimatpåverkan beroende på val av material. Eftersom det går att sänka klimatpåverkan till bibehållen kostnad är klimatsmarta innerväggar förhoppningsvis standard inom en snar framtid.To change climate impact generated by the construction sector, it is of importance to understand the situation of today. January 2022, a new climate-law will require a climate declaration for all new buildings to be produced. The long-term national goal is to achieve zero emissions by 2045. The local initiative LFM30 aims for the construction sector in Malmö to be climate neutral by 2030. There are several ways in which the climate footprint from the construction sector can be reduced. The purpose of this study is to investigate and suggest ways to reduce climate impact on interior walls. Also, to investigate if climate calculations are made today. The study relies on four parts. Calculations on climate impact regarding carbon dioxide equivalents and price. An interview study, a case study on a renovation project and by a literature study. Results from the interviews shed light on difficulties regarding climate calculations during the design of a building. They are time-consuming and resource intensive. Calculations within the study show that stud walls with right configuration can lower the climate impact to more than half. The reduction is due to change in material on studs, isolation and boards. The study states that bio-based insulation materials have a lower climate impact than traditional mineral wool. Also, that wooden studs generate a lower amount of CO2e than steel studs do. Concerning boards, the difference is not distinct between wood-based boards and gypsum boards. Conclusions are that since it’s possible to reduce the climate impact while maintaining cost, climate-smart interior walls can hopefully soon become reality