Jochen Köhler

Norwegian University of Science and Technology | NTNU · Department of Structural Engineering

Lattice systems such as offshore jackets and towers are weight-efficient support structures for wind energy and oil and gas units. Nevertheless, their light-weight is achieved at the expense of increasing their proneness to fatigue failure, due to their many welded connections. Consequently, special attention is to be dedicated to the design of the...

Structural design codes are deliberately kept simple to facilitate the design process. To ensure sufficient safety with simplified models, parameters of these models are often chosen conservatively. This leads to additional “hidden safety” in the design. But what happens if one utilizes more advanced design models without the implicit conservatism...

Fatigue failure risk can be mitigated both by increasing the design fatigue capacity of the structural components and by conducting more frequent inspection and maintenance actions. The optimal combination of these two types of safety measure is structure dependent. It depends, among others, on the relative cost of the safety measures, the conseque...

Fatigue is one of the main failure mechanisms of catenary type mooring lines. Fatigue resistance is affected by a large number of factors. In this paper, the effect of pitting corrosion on the fatigue resistance of mooring lines is empirically estimated. Data from fatigue testing of both new and used chain links are considered. The used chain link...

Mooring systems that are used to secure position keeping of floating offshore oil and gas facilities are subject to deterioration processes, such as pitting corrosion and fatigue crack growth. Past investigations show that pitting corrosion has a significant effect on reducing the fatigue resistance of mooring chain links. In situ inspections are e...

With the ever-increasing popularity of engineered wood products, larger and more complex structures made of timber have been built, such as new tall timber buildings of unprecedented height. Designing for structural robustness in tall timber buildings is still not well understood due the complex properties of timber and the difficulty in testing la...

The different phases of a structure's life-cycle are managed by different teams with little interaction. Correspondingly, the optimization of the individual phases is isolated and does not necessarily result in optimal life-cycle decisions. This motivates the treatment of structural optimization from a broader life-cycle perspective. A framework to...

A critical analysis of the hysteresis models of wooden connections has led to an alternative analytical formulation of the pinching phenomenon. Starting from the generalized Bouc-Wen model, the six-degrees-of-freedom formulation has been extended to an eight parameters formulation, which is a better representative of the connection's cyclical degra...

A more holistic way to look at structural robustness is presented in this paper, using a multi-scale approach. Please contact me for more information.

Monopiles are the most common solution for supporting wind turbines in offshore conditions. At the design phase of a monopile, a frequency check is to be performed to avoid the resonance hazard with the 1P and 3P excitation, i.e. the frequency domains at which the rotor provokes excitations. However, the estimation of the first natural frequency of...

The paper addresses the reliability based calibration of the partial safety factors of semiprobabilistic design codes. The introduced methodology facilitates for the joint consideration of a general domain of design equations. An example calibration of the partial load factors is performed and results and corresponding implications are discussed. A...

This paper contributes to the ongoing discussion on the tentative target reliability levels for the design of structures and calibration of codes. The proposed extension of the existing approaches for code optimisation allows a consistent calibration of codes through all levels of design. The basis is taken from the normative decision theory as the...

To date, our built environment is broadly developed and maintained on the basis of structural design standards. Most design standards contain simplified semi-probabilistic safety concepts that help daily structural engineering decision making using simple calculus. For few projects, the semi-probabilistic safety concept is replaced by advanced prob...

A common approach to define criteria to reliability performance of structures in the development of semi-probabilistic design codes and for probabilistic design of individual structures is to make use of the tentative target reliabilities provided in the JCSS Probabilistic Model Code. An acceptable level of life safety is, however, not guaranteed w...

Connections with metal dowel-type fasteners are important details in timber construction, connecting single members and elements to larger structures. The load-carrying capacity can be described by different failure modes of the fasteners and in the surrounding timber. These failure modes show a dependency on different dimensions and material prope...

This report is a publication of the European Network COST FP1402 Basis of Structural Timber Design - from research to standards. The aim of the Action was to overcome the gap between broadly available scientific results and the specific information needed by designers, industry, authorities and code committees, providing transfer for practical appl...

The performance to withstand biodeterioration of highly insulated walls is evaluated by applying a probabilistic-based methodology that accounts for the involved uncertainties and investigates their significance. Three approaches to representing the outdoor climate are investigated by varying the method and time duration. The temperature-dependent...

A hierarchical model for the variability of material properties in ready-mixed concrete is formulated. The model distinguishes between variation on the batch, recipe, plant, producer, durability class, strength class, and regional standard level. By considering Bayesian inference and maximum likelihood estimators, the contributions from the differe...

The design of cross laminated timber (CLT) structures is not included in the current version of European structural timber design standards of EN 1995 (Eurocode 5, EC 5). Due to the increasing importance of CLT, in different applications such as complete wall or floor elements as well as girders, it is one of the main goals of the currently ongoing...

The performance to withstand biodeterioration of highly insulated walls is evaluated by applying a probabilistic-based methodology that accounts for the involved uncertainties and investigates their significance. Three approaches to representing the outdoor climate are investigated by varying the method and time duration. The temperature-dependent...

The article presents a contribution to the current debate on the probabilistic representation of the wind speed extremes for calibration of the partial safety factor covering wind action. The requirements for the probabilistic model are formulated. The Gumbel distribution is shown to represents best the 10-min mean wind velocity yearly maxima based...

Predicting mould growth on façade constructions during design is important for preventing financial loss, and ensuring a healthy and comfortable indoor environment. Uncertainties in predicting mould growth are related to the representation of the biological phenomenon, the climate exposure and the material uncertainties. This paper proposes a proba...

A framework for calibrating the reliability elements in simplified semi-probabilistic design safety formats is presented. The objective of calibration is to minimize the increase of construction costs, compared to the non-simplified safety format, without reducing the level of structural safety. The framework is utilized for calibrating two simplif...

This paper applies a probabilistic-based approach as a methodology to analyze and compare the mould growth computations’ results from three different mould models. This approach, instead of the conventional deterministic ones, offers the advantage of accounting for uncertainties concerning prediction of mould growth. The results are able to demonst...

This paper systematically reviews mould models that are applicable to wood-based materials. Both similarities and differences are observed with respect to governing factors and their interrelations, methodology, experimental set-ups, substrate and extensiveness, and how the result is communicated. Therefore, a generic framework, representing the ge...

This paper presents a systematic literature review about the development of criteria and models representing mould growth in wood-based materials. First, results from experimental research regarding factors governing mould growth are discussed; afterwards, they are used to analyse the comprehensiveness of current mould models. The review shows subs...

Significant technical advances and developments in the field of timber connections within the last years have fostered the recent renaissance of timber as a structural material. An increased range of connection types and corresponding applications gives designers both opportunity and challenge. The result is a noticeable trend towards systemized so...

Rot decay is one of the problems associated with excessive moisture accumulation in timber façades construction, which can result in financial loss and further intangible consequences. This paper proposes a methodology for cost-optimal design of façades exposed to rot decay. The decay rating is represented by an empirical model as a function of the...

Target safety levels are key elements for reliability-based design and calibration of design codes. They are derived by monetary optimization or from existing codes. The current article discusses these two approaches and proposes a novel method for estimating from existing codes, based on a specific optimality assumption. The method leads to implic...

Monopiles are the most common offshore wind turbine support structures. They are to be designed so that resonance with the rotor-passing excitation is avoided. However, the estimation of the eigenfrequencies is strongly influenced by the soil-structure interaction, whose characterization with prior information is associated with large uncertainties...

In order to make non-linear finite element analyses applicable during assessment of the global resistance of large concrete structures, there is need for a solution strategy with a low modelling uncertainty. A solution strategy comprises choices regarding force equilibrium, kinematic compatibility and constitutive relations. Relatively large solid...

Submerged floating tunnels (SFTs), also known as Archimedes’ bridges, allow crossing waterways where common bridges, underground tunnels or immersed tunnels are not feasible. In spite of this, no SFTs have been built yet in the world except for a prototype in China. The reasons are numerous and widely discussed in literature. The lack of past exper...

Reinforced concrete structures constitute an essential part of the building infrastructure. This infrastructure is aging, and a large number of structures will exceed the prescribed service period in the near future. The aging of concrete structures is often accompanied by corresponding deterioration mechanisms. One of the major deterioration mecha...

Predicting mould occurrence in timber buildings during early-stage design is important for the prevention of social problems and financial loss, and to ensure a healthy and comfortable interior environment. Uncertainties in predicting mould occurrence are twofold ; a) those related to representation of the biological activity involved, and b) those...

Assuming given corrosion states this paper studies the effect of interference of corrosion pits on adjacent rebars on the probability of bending failure of a corroded reinforced concrete beam. Spatial distribution of localised corrosion along a beam is considered in the analyses. The probability of failure is estimated using Monte Carlo simulation....

The fire load has a strong influence on the fire development during a compartment fire and is a significant parameter in fire safety design methods. The assessment of the fire load is therefore an important task in fire safety engineering. This chapter reviews the methods to survey the fire load, discusses how variation during the life time of the...

In this paper, a probabilistic approach for modelling the load-bearing capacity of glued laminated timber is presented. The specific characteristic of this approach is that, at first, timber boards are simulated according the natural growth characteristic of timber. Subsequent, glued laminated timber beams are virtually composed out of the simulate...

The concrete deterioration caused by corrosion is a complex physical, chemical and mechanical process. The modeling of this process is subjected to significant uncertainties, which are based on a simplistic model representation of the actual physical process and limited information on material, environmental and loading characteristics.The present...

In the presented paper, different NDT, SDT and DT inspections methods are introduced and their efficiency in respect to a quantitative estimation of the load-bearing capacity are discussed. Thereby it is particular focused on inspections methods for the estimation of the load-bearing capacity of glued laminated timber. The estimation of the load-be...

Two general approaches may be followed for the development of a fire risk model: statistical models based on observed fire losses can support simple cost-benefit studies but are usually not detailed enough for engineering decision-making. Engineering models, on the other hand, require many assumptions that may result in a biased risk assessment. In...

In the present paper a probabilistic approach for modelling the tensile strength and tensile stiffness properties of timber boards and finger joint connections is presented. The approach includes the geometrical setup of timber boards (the position of knot clusters) and a hierarchical representation of two strength and stiffness related indicators....

Nowadays, the prediction of wire damage caused by fatigue and corrosion is not consistently taken into account for the design of large and unreplaceable cables for suspension or cable-stayed bridges. As a consequence, cables may be overdesigned and not optimized when larger investments in technologically advanced protection systems are applied. In...

Reinforced concrete (RC) structures constitute an essential part of the building infrastructure. This infrastructure is aging and a large number of structures will exceed the prescribed service period in the near future. The aging of concrete structures is often accompanied by corresponding deterioration mechanisms. One of the major deterioration m...

Fire risk models support decision making for engineering problems under the consistent consideration of the associated uncertainties. Empirical approaches can be used for cost-benefit studies when enough data about the decision problem are available. But often the empirical approaches are not detailed enough. Engineering risk models, on the other h...

In the present paper a summary of experimental investigations on GLT beams, having well-known local material properties, is presented. The main objective of the presented project, was the investigations of the influence of varying material properties on the load-bearing behaviour of GLT beams. From altogether 24 GLT beams the load-bearing capacity,...

The occupant load density is a crucial parameter for the design of the means of egress in buildings. In retail buildings the occupant load density is highly influenced by the individual׳s choice and the necessity of a person to visit the store. This causes a high variability of the occupant load density in time. An accurate representation of this v...

In the present paper, a model for the prediction of the local strength and stiffness properties is developed. Compared to existing models, here the local material properties are described according to their morphological characteristics; i.e. the timber boards are subdivided into sections containing knots (knot sections) and sections without knots...

In this paper a framework for updating the load and resistance properties of a partly failed timber construction based on different kind of information is presented. That includes information available, such as the resistance of the failed member(s) or the results of destructive and non-destructive measurements. In accordance to the type of informa...

The present paper reports the results of an investigation regarding the study of the load-carrying capacity of connections with nails of small diameter pneumatically driven in timber-to-timber joints of fast-growing Argentinean Eucalyptus grandis. The effectiveness of the equations provided by Eurocode 5 for calculating the lateral load-carrying ca...

Conference code: 110957, Export Date: 4 September 2015, Correspondence Address: Kohler, J.; Department of Structural Engineering, NTNUNorway, References: Woeste, F.E., Green, D.W., Tarbell, K.A., Marin, L.A., Proof loading to assure lumber strength (1987) Wood Fiber Sci, 19, pp. 283-297;

Conference code: 110957, Export Date: 4 September 2015, References: JCSS Probabilistic Model Code, (2006) Probabilistic Model Code Part III - Resistance Models (3.05 Timber);

The paper presents a probabilistic model characterising tensile strength parallel to grain of Central European spruce boards without longitudinal joints. The effect of length of members on strength is considered explicitly by considering a member by a serial arrangement of weak sections triggered by major knots of knot clusters. In order to demonst...

Conference code: 100885, Export Date: 4 September 2015, Correspondence Address: Norwegian University of Science and Technology, Trondheim, Norway, References: Ceccotti, A., Timber - Concrete composite structures (1995) Timber Engineering - STEP 2, pp. E13/1-12. , (Blass HJ et al. (eds)). Centrum Hout, Almere;

Conference code: 101944, Export Date: 4 September 2015, Correspondence Address: Norwegian University of Science and Technology, Trondheim, Norway, References: Recommendations for the design (1979) Manufacture and Erection of Steel Penstocks of Welded Construction for Hydro Electric Installations, , C.E.C.T. ., E. C. f. B. a. K. S. Structures;

In the present paper the principles of reliability based code calibration are applied to typical design equations for timber structural design in the Eurocode 5. The resulting partial safety factors are discussed in regard to the present practice.

In the present study the influence of knots and their arrangements on the deformation and the failure behaviour is analysed. Therefore, destructive and non-destructive tensile tests are performed. During the tensile tests pictures with a constant frequency are taken. Based on these pictures the relative displacements within knot clusters and thus,...

For the future development of a safe and efficient building infrastructure, it is of utmost importance to learn from past experience. In this paper, a scheme for the evaluation of experience gained from failures and malfunctions in timber structures is developed. It is highlighted that the main motivation to analyse structural failures is to learn...

Conference code: 88343, Cited By :1, Export Date: 4 September 2015, Correspondence Address: Fink, G.; Institute of Structural Engineering, ETH Zurich, Zurich, Switzerland, References: Aicher, S., Höfflin, L., Behrens, W., Determination of local and global modulus of elasticity in wooden boards (2002) Otto-Graf-Journal, 13, pp. 183-198. , 2002;

Conference code: 88343, Cited By :2, Export Date: 4 September 2015, Correspondence Address: Sanctis, G.D.; Institute of Structural Engineering ETH, Zurich, Switzerland, References: Methodik zur Vergleichenden Risikobewertung, , AGB 2005/102 2009:, UVEK Eidgenössisches Departement für Umwelt, Verkehr, Energie und Kommunikation;

The present paper reports on the results of an investigation regarding the determination of the embedding strength of sawn timber of Argentinean Eucalyptus grandis with dowel-type fasteners. The importance of accurately knowing this property has increased with the increasing demand for this material for structural purposes. An empirical research pr...

Structures are planned and designed to fulfill certain requirements in regard to the safety of the users and in regard to the reliability of the fulfillment of the purpose of the structures over the prospected service life. The fulfillment of these requirements is often understood as the performance of the structure. Usually the design follows the...

Reliability analysis of structures for the purpose of code calibration or reliability verification of specific structures requires that the relevant failure modes are represented and analyzed. For structural timber, sustaining a life load, two failure cases for each failure mode have to be considered. These two cases are maximum load level exceedin...

This guideline is prepared within the COST Action E55 “Modelling of the performance of timber structures”, WG3 “Robustness of structures”. The main objective of the Action is to provide the basic framework and knowledge required for the efficient and sustainable use of timber as a structural and building material. Focus is directed on the aspects o...

Conference code: 88343, Export Date: 4 September 2015, Correspondence Address: Faber, M.H.

In timber construction, the last decades were characterized by significant technical advances and developments, widening the range of application of timber structures in the building sector. This resulted in the fact of timber being increasingly used for e.g. wide-span structures. Consequently this led to a growing importance of the assessment of w...

Cross-laminated timber (CLT) is increasingly used in medium-rise timber buildings, for the time being up to eight storeys, among other reasons for cost effectiveness and robustness. This paper presents a simple design model using the effective cross-section method for the structural fire design, i.e. the determination of the mechanical resistance w...

Cross-laminated timber (CLT) is increasingly used in medium-rise timber buildings, for the time being up to eight storeys, among other reasons for cost effectiveness and robustness. This paper presents a simple design model using the effective cross-section method for the structural fire design, i.e. the determination of the mechanical resistance w...

Modern grading machines facilitate the integration of the grading process into the industrialized production scheme with its high demand for production rate. Beside the speed the efficiency of the grading machines depends on the machine's capability to divide the gross supply of ungraded timber into sub-sets of graded timber that fulfil some predef...

Modern applications of structural timber like e.g. in the field of multi-storey domiciles or large span structures require graded timber products with sufficient and in many cases high performing mechanical properties. This can only be reached by means of advanced methods for quality control within the production process of structural timber. In th...

Conference code: 81461, Cited By :2, Export Date: 4 September 2015, Correspondence Address: Schmid, J.; SP Trätek, Drottning Kristinas väg 67, 11428 Stockholm, Sweden, References: Eurocode 5: Design of timber structures-Part 1-2: General-Structural fire design (2004) European Standard, , EN 1995-1-2, European Committee for Standardization, Brussels...

Moisture interaction with timber structures will already at normal indoor conditions have influence on the stress state of the timber. In some cases moisture induced stress will be of such magnitude that the performance of the structure will not live up to the safety or serviceability standards required of the structure. Moisture interaction with t...

The safe and sustainable use of materials in construction necessitates that the life-cycle performance of structures can be predicted and reassessed with sufficient accuracy. Recent research achievements in the field of materials science and structural reliability provide a framework for the quantification of safety, durability and life-cycle costs...

These days there are many discussions about applicability and efficiency of the existing grading procedures for machine strength grading of structural timber given in the European Standard EN 14081. Different alternative grading strategies have been proposed, all of them dealing with statistical frameworks to control timber grading procedures in a...