Investigation into the stress/strain state of a big bay frame considering support settlement

Abstract

A calculation model of a building is only a simulation of the individual properties of the construction. Such a model is expressed by many factors, the most important of which are experience and knowledge of a designer. In difference to a traditional “single-stage” solution, an effective numerical analysis of a complicated situation can be presented comparing a few different variants. Such situation is specific for high-technology industrial facilities or entertainment buildings. A typical simulation sequence cannot be used for original buildings with principally different properties because investigation should take into account features of the construction. A general solution should analyze the already existing technical possibility and an individual situation considering the qualification of engineering staff. The paper presents investigation into a transversal frame of an indoor slope of the complex facility “Ski Slopes Covered With Snow Pavement in Druskininkai, Lithuania” carried out in 2009. According to the current Eurocodes and Lithuanian design codes, the service life of the facility is 100 years and a class of responsibility is RC3. The frame has a bay of 51,5 m, columns with foundations and a truss are rigidly jointed, the middle height of the frame (depending on the angle of the slope along facility) is about 1/3 of the bay. The stiffness of all structural members is specified. For frame actions and structural design, valid design codes are used. In geomorphologic meaning, the building site is placed near (about 100 m) the river Nemunas where real difference in the altitudes of the ground initial surface makes about 40 m. On the basis of the analyzed situation in the site, a decision on making a foundation with a pile cap on displacement piles has been accepted. Each pile consists of two parts: the upper part is of 600 mm diameter and 2 m length, whereas the last one has a diameter of 380 mm. After pile mounting, the steel shell of the pipe is pulled out. For an analytical analysis of a single pile, the Vesic formula is applied. Under conditions that two piles of the building site have been tested by means of vertical load action, two pairs of piles have followed the horizontal one. Vertical 1044 kN and horizontal 120 kN test loadings have been divided into 6 equal stages. Two asymmetrical foundations of the transversal frame are designed differently and make 8 piles in axis “A” and 6 piles - in “E”. Three variants of the pile calculation model are considered: node support, one finite element (an upper part of the pile) on the elastic spring in the vertical direction at the bottom edge and a pile divided into two parts on the vertical elastic spring at the bottom edge and along it (a horizontal subgrade factor). Within a course of investigation, the pile cap is modelled applying shell finite elements while the piles - employing beam ones. The final decision about frame stress/strain state can be made on the basis of analyzing the general calculation model “over-ground frame/foundation/ground”. Thus, three new models, including 5, 6 and 7 present foundations are jointed by the over-ground frame. In these cases, the columns with the truss are subjected not only to static loads but also to kinematic actions, i. e. foundation settlements, rotations and lateral displacements. A comparison of the results of seven separate calculation models shows that support parts of the columns are loaded low in case of elastic subgrade on the piles; bending the pile cap is the same; the distribution of internal forces between foundations in case of piles is more “soft”. Conclusions and recommendations are provided.

Article in Lithuanian.

Plokščiojo didelio tarpatramio rėmo įtemptojo ir deformuotojo būvio tyrimas, atsižvelgiant į atramų poslinkius

Santrauka. Pateiktas didelio tarpatramio skersinio rėmo įtemptojo ir deformuotojo būvio tyrimas, kai, be įprastinių statinių apkrovų, rėmą veikia pamatų nuosėdžiai, deviacijos bei skečiamieji poslinkiai. Poliniai rėmo pamatai skaičiuojami analitiškai ir modeliuojami skaitiškai taikant įvairias inžinerines prielaidas. Siekiant nustatyti tikslius duomenis apie mechaninį polių deformavimą statybos vietovės sąlygomis, atlikti polių bandymai vertikaliosiomis bei horizontaliosiomis apkrovomis. Straipsnyje gretinami septyni alternatyvūs polių modeliavimo variantai, modeliuojama antžeminė rėmo dalis su poliniais pamatais ant tampraus pagrindo (vertikaliąja ir horizontaliąja kryptimis). Išsamūs skersinio rėmo mechaninio būvio tyrimai parodė, kad kolonų atraminiai pjūviai mažiau lenkiami sprendžiant bendrąjį uždavinį (rėmas su pamatais), nei skaičiuojant antžeminę ir požeminę rėmo dalis atskirai, rostverkų įrąžos pasiskirsto panašiai skirtingais atvejais, poliai sprendžiant bendrąjį uždavinį ašine jėga apkrauti daugiau, bet mažiau lenkiami. Nagrinėjant sudėtingus uždavinius su netradiciniais sprendiniais, reikia tirti kelis skaičiuojamosios schemos variantus, sudarytus taikant iš principo skirtingas prielaidas.

Reikšminiai žodžiai: atramų poslinkiai, poliniai pamatai, natūriniai bandymai.

First Published Online: 16 May 2013

Keyword : settlements, pile foundations, natural tests