Search the digital library catalog

Abstract: A nonlinear semi-numeric and finite element analysis of three-point bending tests of notched polymer fiber-reinforced concrete prisms was performed. The computational and experimental results were compared in terms of the load-displacement behavior. The vertical midspan displacement and the crack mouth opening displacement results were considered. The nonlinear semi-numeric computational procedure involved the moment-curvature relation, calculated by considering the constitutive material law from the fib Model Code for Concrete Structures 2010, and considered a plastic hinge mechanism to simulate the cracked region behavior. Two sets of tensile mechanical properties were considered for the constitutive material law: back-calculated (by an inverse analysis) tensile strength properties from the experimental results, and tensile strength properties calculated by simplified expressions from the fib Model Code for Concrete Structures 2010. Other mechanical properties were determined by additional compressive tests and standard relations for the dependency of various mechanical properties on the concrete compressive strength. The nonlinear finite element analysis incorporated the Menetrey-Willam material model to simulate the fiber-reinforced concrete behavior. The nonlinear semi-numeric analysis load-displacement results based on the back-calculated tensile strength properties relatively accurately matched with the experimental results, whereas the nonlinear semi-numeric analysis load-displacement results based on tensile strength properties calculated by simplified expressions from the fib Model Code for Concrete Structures 2010 and the nonlinear finite element analysis load-displacement results showed certain shortcomings.
Keywords: polymer fiber-reinforced concrete, moment-curvature relation, nonlinear plastic hinge, load-displacement relation, crack width, nonlinear analysis, finite element analysis, Menetrey-Willam material model, three-point bending test, compressive test
Published in DKUM: 19.02.2024; Views: 350; Downloads: 29
Full text (6,91 MB)
This document has many files! More...

Abstract: In addition to vertical axial loads, the footings of structures are often subjected to eccentric loads caused by the forces of earth pressures, earthquakes, water, wind, etc. Due to eccentric loading, the two edges settle by different amounts, causing the footing to tilt and then the pressure below the footing does not remain uniform. The T-shape is proposed as a footing shape for improving the bearing capacity of shallow footings against the action of eccentric loads. The vertical insertion of the rigid T-shaped footing, into the bearing soil, provides considerable resistance, against both of sliding and overturning, enough to regain the reduction in bearing capacity and increase in settlement. In this study, a series of experimental and numerical results from the ultimate loads and settlement of T-shaped footings are reported. A total of 48 model tests were conducted for investigating the effects of different parameters, such as the problem geometry and soil density. The problem geometry was represented by two parameters, the load eccentricity (e) and the insertion depth (H) of the T-shape into the loose and dense sand soil. After the experimental stage, the numerical analyses were carried out using a plane strain, two-dimensional, finite-element-based computer program. The behaviour of the T-shape footing on sand beds is represented by the hardening soil model. The results of the experimental and numerical studies proved that the ultimate bearing capacity of a footing under eccentric loads could be improved by inserting a vertical central cut-off rigidly connected to the footing bottom. The load settlement curves indicate that the higher load eccentricity results in a decrease in the bearing capacity of the strip footing. It was also proved that the ultimate bearing capacity values can, depending on the soil density, be improved by up to four times that of the loose sand case. This investigation is considered to have provided a useful basis for further research, leading to an increased understanding of the T-shaped footing design.
Keywords: model test, finite-element method, T-shaped footing, eccentric loading, sand
Published in DKUM: 14.06.2018; Views: 1283; Downloads: 59
Full text (686,03 KB)
This document has many files! More...

Abstract: Naredili smo celovito študijo s podatki iz članka (Koder et al., 2015) in doktorata (Koder, Silvo 2015). Namen naše raziskave je bila uporaba različnih statističnih pristopov (t-test neodvisnih vzorcev, anova, test dveh neodvisnih vzorcev, test k neodvisnih vzorcev, korelacije, linearna in logistična regresija) in z njimi odkriti povezave med biokemijskimi, kliničnimi in genetskimi podatki z odzivom na zdravljenje bolnikov s CB z adalimumabom. Uporabili smo programsko orodje SPSS in test normalne porazdelitve ShapiroWilk za izvedbo statističnih analiz. Odziv smo merili z vprašalnikom IBDQ in biokemijskim parametrom C-reaktivni protein (CRP). Za vsakega pacienta (N = 97) smo beležili 24 biokemijskih, 34 kliničnih in 34 genetskih podatkov. S kliničnim odzivom IBDQ se je dvakrat ponovilo pet polimorfizmov pri posameznemu genu. Trikrat so se ponovili trije biokemijski in šest kliničnih parametrov. Najbolj signifikantne povezave smo zaznali s PTGER4, CASP9, CCNY, sakroileitisom in alkalno fosfatazo. Z biološkim odzivom CRP se je dvakrat ponovilo devet povezav s polimorfizmi pri posameznem genu. Trikrat sta se ponovila dva biokemijska in eden klinični parameter. Za najbolj signifikantne so se izkazale povezave z ATG16L1, IL27, NR1|2 in c11orf30 ter albuminom. Z uporabo linearne in logistične (binarne) regresije smo izdelali napovedne modele za IBDQ in CRP. Z linearno regresijo smo dobili model z najvišjim R2 (0,691) za IBDQ v tridesetem tednu (natančnost: 69,32 %). Medtem ko smo najboljšo natančnost dobili za IBDQ v dvanajstem (76,00 %, R2 = 0,619) in dvajsetem (75,68 %, R2 = 0,567) tednu. Modeli za CRP so imeli R2 nad 0,980, vendar je njihova natančnost pod 61 %. Pri logistični regresiji je največjo natančnost imel model za IBDQ v četrtem tednu (R2 = 0,912; natančnost: 81,48 %). Natančnost modelov za odziv v dvanajstem (R2 = 0,482), dvajsetem (R2 = 0,465) in tridesetem (R2 = 0,653) tednu je znašala 71,43 %, 68,75 % in 64,10 %. Natančnost modelov za odziv CRP je znašala nad 70 %, vendar je to posledica manjkajočih podatkov in s tem manj veljavnih vzorcev. Ob koncu študije smo izdelali tabelo, s katero smo predstavili izbiro statističnega testa glede na biokemijske, klinične in genetske podatke.
Keywords: Crohnova bolezen, adalimumab, statistične metode, Mann-Whitney, Fisher's Exact test, Chi square test, test neodvisnih vzorcev, linearna regresija, logistična regresija, napovedni model
Published in DKUM: 22.10.2015; Views: 2259; Downloads: 326
Full text (2,47 MB)