B.L. Deam

“Multi-storey prestressed timber buildings in New Zealand.”

This paper describes recent research and development of a new system for multi-storey prestressed timber buildings in New Zealand. The new system gives opportunities for much greater use of timber and engineered wood products in large buildings, using innovative technologies for creating high-quality buildings with large open spaces, excellent living and working environments, and resistance to hazards such as earthquakes, fires and extreme weather events.

Real-Time System Identification of a Nonlinear Four-Story Steel Frame Structure—Application to Structural Health Monitoring

Structural health monitoring (SHM) is a means of identifying damage from structural response to environmental loads. Real-time SHM is of particular use for rapid assessment of structural safety by owners and civil defense authorities. This paper presents an algorithm for real-time SHM during earthquake events using only acceleration measurements and infrequently measured displacement motivated by global positioning system. The algorithm identifies a nonlinear baseline model including hysteretic dynamics and permanent deformation using convex integral-based fitting methods and piecewise linear least squares fitting. The methodology identifies pre and postyield stiffness, elastic and plastic components of displacement, and final residual displacement. It thus identifies key measures of damage affecting the immediate safety or use of the structure and the long-term cost of repair and retrofit. The algorithm is tested with simulated response data using the El-Centro earthquake record and with measured response data. Both data sets are based on a four-story nonlinear steel frame structure using the El-Centro ground motion record. Overall, the algorithm is shown to provide accurate indications of the existence, location, and magnitude of structural damage for nonlinear shear-type buildings. Additionally, the identified permanent displacement is a particularly useful damage measure for the construction of probabilistic fragility functions.

Analytical cracking load estimation of Laminated Veneer Lumber (LVL) beams with holes

Predicting the load-carrying capacity of timber beams with holes cannot be performed by usual analysis methods if the failure of the beam is governed by the crack initiation and propagation around the hole at low load levels. Predicting the cracking load is an important design issue because it corresponds to the load-carrying capacity of the timber beam before the crack propagation. One of the models that can be used for the fracture formulation is that of a beam on elastic foundation. In this model a part of the beam is assumed to follow the conditions of beam with elastic foundation which has spring stiffness equal to the fracture properties of the material in the crack surface. Based on beam on elastic foundation model, the cracking load prediction is the target of the paper. Some closed form solutions for the beam with hole are presented. The formulation has been derived for two cases of pure shear and pure bending moment. Finally a semi-empirical formulation for combination of shear and bending moment in the section is presented. The model predictions are compared with the results of an experimental program showing good correlation. The analytical model can therefore be proposed for future revisions of codes of practice such as the Eurocode 5.ZusammenfassungDie Tragfähigkeit von Holzbalken mit Durchbrüchen kann nicht mit herkömmlichen Methoden bestimmt werden, wenn der Bruch darauf zurückzuführen ist, dass am Durchbruch ein Riss bei einer geringen Belastung entsteht und sich fortpflanzt. Die Bestimmung der Risslast, d.h. der Last bei der Entstehung des Risses, ist ein wichtiger Bemessungsaspekt, da sie die Tragfähigkeit des Holzbalkens vor der Rissfortpflanzung angibt. Eines der Modelle, das für die Bruchformulierung verwendet werden kann, ist das des elastisch gebetteten Balkens. In diesem Modell wird davon ausgegangen, dass ein Teil des Balkens einem elastisch gebetteten Balken entspricht, wobei die Federsteifigkeit den Brucheigenschaften des Materials in der Rissfläche entspricht. Ziel dieser Arbeit ist die Bestimmung der Risslast unter Verwendung des Modells des elastisch gebetteten Balkens. Es werden einige geschlossene Lösungen für einen Balken mit Durchbruch vorgestellt. Die Formulierung wird für die zwei Fälle reiner Schub- und reiner Biegebeanspruchung hergeleitet. Weiterhin wird eine halbempirische Formulierung für eine Kombination von Schub- und Biegebeanspruchung dargestellt. Die Modellvorhersagen werden mit den Ergebnissen eines Versuchsprogramms verglichen und zeigen eine gute Korrelation. Aus diesem Grund kann das analytische Modell zur Verwendung für zukünftige Revisionen anerkannter technischer Regeln wie zum Beispiel dem Eurocode 5 vorgeschlagen werden.