The analysis of steel and composite frames has traditionally been carried out by
idealizing beam-to-column connections as either rigid or pinned. Although some
advanced analysis methods have been proposed to account for semi-rigid connections, the
performance of these methods strongly depends on the proper modeling of connection
behavior. The primary challenge of modeling beam-to-column connections is their
inelastic response and continuously varying stiffness, strength, and ductility. In this report,
two distinct approaches???mathematical models and informational models???are proposed
to account for the complex hysteretic behavior of beam-to-column connections. The
performance of the two approaches is examined and is then followed by a discussion of
their merits and deficiencies. To capitalize on the merits of both mathematical and
informational representations, a new approach, a hybrid modeling framework, is
developed and demonstrated through modeling beam-to-column connections.
Component-based modeling is a compromise spanning two extremes in the field
of mathematical modeling: simplified global models and finite element models. In the
component-based modeling of angle connections, the five critical components of
excessive deformation are identified. Constitutive relationships of angles, column panel
zones, and contact between angles and column flanges, are derived by using only
material and geometric properties and theoretical mechanics considerations. Those of slip
and bolt hole ovalization are simplified by empirically-suggested mathematical
representation and expert opinions. A mathematical model is then assembled as a macroelement
by combining rigid bars and springs that represent the constitutive relationship of
components. Lastly, the moment-rotation curves of the mathematical models are
compared with those of experimental tests. In the case of a top-and-seat angle connection
with double web angles, a pinched hysteretic response is predicted quite well by complete
mechanical models, which take advantage of only material and geometric properties. On
the other hand, to exhibit the highly pinched behavior of a top-and-seat angle connection
without web angles, a mathematical model requires components of slip and bolt hole
ovalization, which are more amenable to informational modeling.
An alternative method is informational modeling, which constitutes a fundamental
shift from mathematical equations to data that contain the required information about
underlying mechanics. The information is extracted from observed data and stored in
neural networks. Two different training data sets, analytically-generated and
experimental data, are tested to examine the performance of informational models. Both
informational models show acceptable agreement with the moment-rotation curves of the
experiments. Adding a degradation parameter improves the informational models when
modeling highly pinched hysteretic behavior. However, informational models cannot
represent the contribution of individual components and therefore do not provide an
insight into the underlying mechanics of components.
In this study, a new hybrid modeling framework is proposed. In the hybrid
framework, a conventional mathematical model is complemented by the informational
methods. The basic premise of the proposed hybrid methodology is that not all features of
system response are amenable to mathematical modeling, hence considering
informational alternatives. This may be because (i) the underlying theory is not available
or not sufficiently developed, or (ii) the existing theory is too complex and therefore not
suitable for modeling within building frame analysis. The role of informational methods
is to model aspects that the mathematical model leaves out. Autoprogressive algorithm
and self-learning simulation extract the missing aspects from a system response. In a
hybrid framework, experimental data is an integral part of modeling, rather than being
used strictly for validation processes. The potential of the hybrid methodology is
illustrated through modeling complex hysteretic behavior of beam-to-column connections.
Mechanics-based components of deformation such as angles, flange-plates, and column
panel zone, are idealized to a mathematical model by using a complete mechanical
approach. Although the mathematical model represents envelope curves in terms of initial
stiffness and yielding strength, it is not capable of capturing the pinching effects.
Pinching is caused mainly by separation between angles and column flanges as well as
slip between angles/flange-plates and beam flanges. These components of deformation
are suitable for informational modeling. Finally, the moment-rotation curves of the
hybrid models are validated with those of the experimental tests. The comparison shows
that the hybrid models are capable of representing the highly pinched hysteretic behavior
of beam-to-column connections. In addition, the developed hybrid model is successfully
used to predict the behavior of a newly-designed connection.unpublishednot peer reviewe