**1. Introduction**

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Nowadays steel and composite (steel-concrete) building structures are more and more be‐ coming the modern landmarks of urban areas. Designers seem to continuously move the safety border, in order to increase slenderness and lightness of their structural systems. However, more and more steel and composite floors are carried out as light weight struc‐ tures with low frequencies and low damping. These facts have generated very slender com‐ posite floors, sensitive to dynamic excitation, and consequently changed the serviceability and ultimate limit states associated to their design.

A direct consequence of this new design trend is a considerable increase in problems re‐ lated to unwanted composite floor vibrations. For this reason, the structural floors sys‐ tems become vulnerable to excessive vibrations produced by impacts such as human rhythmic activities. On the other hand, the increasing incidence of building vibration problems due to human activities led to a specific design criterion to be addressed in structural design [1-7]. This was the main motivation for the development of a design methodology centred on the steel-concrete composite floors non-linear dynamic response submitted to loads due to human rhythmic activities.

Considering all aspects mentioned before, the main objective of this paper is to investigate the beam-to-beam connections effect (rigid, semi-rigid and flexible) and the influence of steel-concrete interaction degree (from total to various levels of partial interaction) over the non-linear dynamic behaviour of composite floors when subjected to human rhythmic activ‐ ities [1,2]. This way, the dynamic loads were obtained through experimental tests with indi‐ viduals carrying out rhythmic and non-rhythmic activities such as stimulated and nonstimulated jumping and aerobic gymnastics [7]. Based on the experimental results, human load functions due to rhythmic and non-rhythmic activities are proposed [7].

dynamic load [1-6]. The dynamic analysis is performed equating one of the activity harmon‐

An Analysis of the Beam-to-Beam Connections Effect and Steel-Concrete Interaction Degree Over the Composite

This study have considered the dynamic loads obtained by Faisca [7], based on the results achieved through a long series of experimental tests with individuals carrying out rhythmic and non-rhythmic activities. The dynamic loads generated by human rhythmic activities,

The loading modelling was able to simulate human activities like aerobics, dancing and free jumps. In this paper, the Hanning function was used to represent the human dynamic actions. The Hanning function was used since it was verified that this mathematical representation is very similar to the signal force obtained through experimental tests developed by Faisca [7].

The mathematical representation of the human dynamic loading using the Hanning func‐ tion is given by Equation (1) and illustrated in Figure 1. The required parameters for the use of Equation (1) are related to the activity period, T, contact period with the structure, Tc, pe‐ riod without contact with the model, Ts, impact coefficient, Kp, and phase coefficient, CD. Figure 2 and the Table 1 illustrate the phase coefficient variation, CD, for human activities studied by Faisca [7], considering a certain number of individuals and later extrapolated for large number of peoples. Table 2 presents the experimental parameters used for human rhythmic activities representation and Figure 3 presents examples of dynamic action related

<sup>2</sup> ( ) 0.5 0.5cos

*F t CD K P t*

ì ü ï ï é ù æ ö

<sup>=</sup> í ý ê ú - ç ÷ ï ï î þ ë û è ø

*c*

(1)

http://dx.doi.org/10.5772/51672

285

p

*T*

*p*

ics to the floor fundamental frequency, leading to resonance.

to human rhythmic activities investigated in this work.

() 0

=

*F t*

When *t* ≤*Tc*

Where:

t: time (s);

When *Tc* ≤*t* ≤*T*

F(t): dynamic loading (N);

Tc: activity contact period (s);

T: activity period (s);

P: person's weight (N);

Kp: impact coefficient;

CD: phase coefficient

such as jumps, aerobics and dancing were investigated by Faisca [7].

The investigated structural model was based on a steel-concrete composite floor spanning 40m by 40m, with a total area of 1600m2 . The structural system consisted of a typical compo‐ site floor of a commercial building. The composite floor studied in this work is supported by steel columns and is currently submitted to human rhythmic loads. The structural system is constituted of composite girders and a 100mm thick concrete slab [1,2].

The proposed computational model adopted the usual mesh refinement techniques present in finite element method simulations, based on the ANSYS program [8]. This numerical model enabled a complete dynamic evaluation of the investigated steel-concrete composite floor es‐ pecially in terms of human comfort and its associated vibration serviceability limit states.

Initially, all the composite floor natural frequencies and vibration modes were obtained. In sequence, based on an extensive parametric study, the floor dynamic response in terms of peak accelerations was obtained and compared to the limiting values proposed by several authors and design codes [6,9]. An extensive parametric analysis was developed focusing in the evaluation of the beam-to-beam connections effect and the influence of steel-concrete in‐ teraction degree over the investigated composite floor non-linear dynamic response, when submitted to human rhythmic activities.

The structural system peak accelerations were compared to the limiting values proposed by several authors and design standards [6,9]. The current investigation indicated that human rhythmic activities could induce the steel-concrete composite floors to reach unacceptable vibration levels and, in these situations, lead to a violation of the current human comfort cri‐ teria for these specific structures.
